Reland of "Fix URL clipping on iOS 11."

This reverts CL 779191.

Wraps omnibox textfield into a container that positions the textfield
inside of itself and clips its bounds so that the optimal clipping is
used. The clipping logic replicates that of the pre-iOS 11 solution
with UITextField overrides that are now broken in iOS 11.
To mask the clipped ends of the omnibox, a ClippingMaskView is used
as a maskView of the clipping view.
All of this is behind kClippingTextfield flag that is enabled by
default.

Bug: 749788
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I4cc6673200a8fbdc57451dc9120dfd4eeec5a853
Reviewed-on: https://chromium-review.googlesource.com/844079
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526693}

ios/chrome/browser/BUILD.gn

@@ -127,6 +127,7 @@ source_set("browser") {
     "//ios/chrome/browser/ui/fullscreen",
     "//ios/chrome/browser/ui/history:history_base_feature",
     "//ios/chrome/browser/ui/main:feature_flags",
+    "//ios/chrome/browser/ui/omnibox",
     "//ios/chrome/browser/ui/toolbar:feature",
     "//ios/chrome/browser/ui/toolbar/public:toolbar_base_feature",
     "//ios/chrome/common",

ios/chrome/browser/about_flags.mm

@@ -46,6 +46,7 @@
 #include "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
 #import "ios/chrome/browser/ui/history/history_base_feature.h"
 #include "ios/chrome/browser/ui/main/main_feature_flags.h"
+#import "ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h"
 #import "ios/chrome/browser/ui/toolbar/public/toolbar_controller_base_feature.h"
 #import "ios/chrome/browser/ui/toolbar/toolbar_private_base_feature.h"
 #include "ios/chrome/grit/ios_strings.h"
@@ -185,6 +186,9 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
     {"clean-toolbar", flag_descriptions::kCleanToolbarName,
      flag_descriptions::kCleanToolbarDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kCleanToolbar)},
+    {"clipping-textfield", flag_descriptions::kClippingTextfieldName,
+     flag_descriptions::kClippingTextfieldDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(kClippingTextfield)},
     {"bookmark-new-edit-page", flag_descriptions::kBookmarkNewEditPageName,
      flag_descriptions::kBookmarkNewEditPageDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kBookmarkNewEditPage)},

ios/chrome/browser/ios_chrome_flag_descriptions.cc

@@ -35,6 +35,11 @@ const char kCleanToolbarDescription[] =
     "When enabled, the Clean Toolbar will be used instead of "
     "WebToolbarController.";
 
+const char kClippingTextfieldName[] = "Clipping Textfield";
+const char kClippingTextfieldDescription[] =
+    "When enabled, the new URL clipping implementation compatible with iOS 11 "
+    "is used.";
+
 const char kContextualSearch[] = "Contextual Search";
 const char kContextualSearchDescription[] =
     "Whether or not Contextual Search is enabled.";

ios/chrome/browser/ios_chrome_flag_descriptions.h

@@ -29,6 +29,10 @@ extern const char kCaptivePortalDescription[];
 extern const char kCleanToolbarName[];
 extern const char kCleanToolbarDescription[];
 
+// Title and description for the flag to enable Omnibox Clipping.
+extern const char kClippingTextfieldName[];
+extern const char kClippingTextfieldDescription[];
+
 // Title and description for the flag to enable Contextual Search.
 extern const char kContextualSearch[];
 extern const char kContextualSearchDescription[];

ios/chrome/browser/ui/location_bar/location_bar_view.mm

@@ -5,6 +5,8 @@
 #import "ios/chrome/browser/ui/location_bar/location_bar_view.h"
 
 #import "ios/chrome/browser/ui/animation_util.h"
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield_container.h"
+#import "ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h"
 #import "ios/chrome/browser/ui/omnibox/omnibox_text_field_ios.h"
 #import "ios/chrome/browser/ui/toolbar/public/web_toolbar_controller_constants.h"
 #include "ios/chrome/browser/ui/ui_util.h"
@@ -60,6 +62,10 @@ const CGFloat kTextFieldLeadingOffsetImage = 6;
 // When the |leadingButton| is not hidden, this is a constraint that links the
 // leading edge of the button to self leading edge. Used for animations.
 @property(nonatomic, strong) NSLayoutConstraint* leadingButtonLeadingConstraint;
+// The textfield container. The |textField| is contained in it, and its frame
+// should not be managed directly, instead the location bar uses this container.
+// This is required to achieve desired text clipping of long URLs.
+@property(nonatomic, strong) ClippingTextFieldContainer* textFieldContainer;
 @end
 
 @implementation LocationBarView
@@ -68,6 +74,7 @@ const CGFloat kTextFieldLeadingOffsetImage = 6;
 @synthesize leadingTextfieldConstraint = _leadingTextfieldConstraint;
 @synthesize incognito = _incognito;
 @synthesize leadingButtonLeadingConstraint = _leadingButtonLeadingConstraint;
+@synthesize textFieldContainer = _textFieldContainer;
 
 #pragma mark - Public properties
 
@@ -98,20 +105,55 @@ const CGFloat kTextFieldLeadingOffsetImage = 6;
                                                        font:font
                                                   textColor:textColor
                                                   tintColor:tintColor];
-    [self addSubview:_textField];
 
-    _leadingTextfieldConstraint = [_textField.leadingAnchor
-        constraintEqualToAnchor:self.leadingAnchor
-                       constant:kTextFieldLeadingOffsetNoImage];
-
-    [NSLayoutConstraint activateConstraints:@[
-      [_textField.trailingAnchor constraintEqualToAnchor:self.trailingAnchor],
-      [_textField.topAnchor constraintEqualToAnchor:self.topAnchor],
-      [_textField.bottomAnchor constraintEqualToAnchor:self.bottomAnchor],
-      _leadingTextfieldConstraint,
-    ]];
-
-    _textField.translatesAutoresizingMaskIntoConstraints = NO;
+    if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+      // When clipping is enabled, the text field is put into a container.
+
+      // TODO(crbug.com/789968): remove these insets when the location bar
+      // background is managed by this view and not toolbar controller. These
+      // insets allow the gradient masking of the omnibox to not extend beyond
+      // the omnibox background's visible frame.
+      self.layoutMargins = UIEdgeInsetsMake(3, 3, 3, 3);
+
+      _textFieldContainer = [[ClippingTextFieldContainer alloc]
+          initWithClippingTextField:_textField];
+      [self addSubview:_textFieldContainer];
+
+      _leadingTextfieldConstraint = [_textFieldContainer.leadingAnchor
+          constraintEqualToAnchor:self.leadingAnchor
+                         constant:kTextFieldLeadingOffsetNoImage];
+
+      [NSLayoutConstraint activateConstraints:@[
+        [_textFieldContainer.trailingAnchor
+            constraintEqualToAnchor:self.layoutMarginsGuide.trailingAnchor],
+        [_textFieldContainer.topAnchor
+            constraintEqualToAnchor:self.layoutMarginsGuide.topAnchor],
+        [_textFieldContainer.bottomAnchor
+            constraintEqualToAnchor:self.layoutMarginsGuide.bottomAnchor],
+        _leadingTextfieldConstraint,
+      ]];
+
+      _textFieldContainer.translatesAutoresizingMaskIntoConstraints = NO;
+      [_textFieldContainer
+          setContentCompressionResistancePriority:UILayoutPriorityDefaultLow
+                                          forAxis:
+                                              UILayoutConstraintAxisHorizontal];
+    } else {
+      // Contain the text field directly, with no clipping container.
+      [self addSubview:_textField];
+      _leadingTextfieldConstraint = [_textField.leadingAnchor
+          constraintEqualToAnchor:self.leadingAnchor
+                         constant:kTextFieldLeadingOffsetNoImage];
+
+      [NSLayoutConstraint activateConstraints:@[
+        [_textField.trailingAnchor constraintEqualToAnchor:self.trailingAnchor],
+        [_textField.topAnchor constraintEqualToAnchor:self.topAnchor],
+        [_textField.bottomAnchor constraintEqualToAnchor:self.bottomAnchor],
+        _leadingTextfieldConstraint,
+      ]];
+
+      _textField.translatesAutoresizingMaskIntoConstraints = NO;
+    }
   }
   return self;
 }
@@ -127,15 +169,26 @@ const CGFloat kTextFieldLeadingOffsetImage = 6;
   } else {
     [self addSubview:_leadingButton];
     self.leadingTextfieldConstraint.active = NO;
-    self.leadingButtonLeadingConstraint = [self.leadingAnchor
+    self.leadingButtonLeadingConstraint = [self.layoutMarginsGuide.leadingAnchor
         constraintEqualToAnchor:self.leadingButton.leadingAnchor
                        constant:-kLeadingButtonEdgeOffset];
+
+    NSLayoutConstraint* leadingButtonToTextField = nil;
+    if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+      leadingButtonToTextField = [self.leadingButton.trailingAnchor
+          constraintEqualToAnchor:self.textFieldContainer.leadingAnchor
+                         constant:-kTextFieldLeadingOffsetImage];
+    } else {
+      leadingButtonToTextField = [self.leadingButton.trailingAnchor
+          constraintEqualToAnchor:self.textField.leadingAnchor
+                         constant:-kTextFieldLeadingOffsetImage];
+    }
+
     [NSLayoutConstraint activateConstraints:@[
-      [_leadingButton.centerYAnchor constraintEqualToAnchor:self.centerYAnchor],
+      [_leadingButton.centerYAnchor
+          constraintEqualToAnchor:self.layoutMarginsGuide.centerYAnchor],
       self.leadingButtonLeadingConstraint,
-      [self.leadingButton.trailingAnchor
-          constraintEqualToAnchor:self.textField.leadingAnchor
-                         constant:-kTextFieldLeadingOffsetImage],
+      leadingButtonToTextField,
     ]];
   }
 }

ios/chrome/browser/ui/omnibox/BUILD.gn

@@ -7,6 +7,8 @@ source_set("omnibox") {
     "location_bar_controller.cc",
     "location_bar_controller.h",
     "location_bar_delegate.h",
+    "omnibox_clipping_feature.h",
+    "omnibox_clipping_feature.mm",
     "web_omnibox_edit_controller.cc",
     "web_omnibox_edit_controller.h",
   ]
@@ -39,6 +41,12 @@ source_set("omnibox_internal") {
     "autocomplete_suggestion.h",
     "chrome_omnibox_client_ios.h",
     "chrome_omnibox_client_ios.mm",
+    "clipping_mask_view.h",
+    "clipping_mask_view.mm",
+    "clipping_textfield.h",
+    "clipping_textfield.mm",
+    "clipping_textfield_container.h",
+    "clipping_textfield_container.mm",
     "image_retriever.h",
     "location_bar_controller_impl.h",
     "location_bar_controller_impl.mm",
@@ -128,9 +136,11 @@ source_set("unit_tests") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
+    "clipping_textfield_container_unittest.mm",
     "omnibox_text_field_ios_unittest.mm",
   ]
   deps = [
+    ":omnibox",
     ":omnibox_internal",
     ":resources_unit_tests",
     "//base",

ios/chrome/browser/ui/omnibox/clipping_mask_view.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_MASK_VIEW_H_
+#define IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_MASK_VIEW_H_
+
+#import <UIKit/UIKit.h>
+
+// The view used as a mask when the omnibox textfield is being clipped.
+// Displays an opaque rectangle with left, right, or both edges being
+// faded out with transparent gradient.
+@interface ClippingMaskView : UIView
+
+// Whether the left edge is faded.
+@property(nonatomic, assign) BOOL fadeLeft;
+// Whether the right edge is faded.
+@property(nonatomic, assign) BOOL fadeRight;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_MASK_VIEW_H_

ios/chrome/browser/ui/omnibox/clipping_mask_view.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/omnibox/clipping_mask_view.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+#pragma mark - GradientView
+
+namespace {
+
+enum GradientViewDirection {
+  GRADIENT_LEFT_TO_RIGHT,
+  GRADIENT_RIGHT_TO_LEFT,
+};
+
+}  // namespace
+
+// The gradient view is a view that displays a simple horizontal gradient, from
+// black to transparent.
+@interface GradientView : UIView
+// Sets the gradient's direction. You have to call this at least once to
+// configure the gradient.
+@property(nonatomic, assign) GradientViewDirection direction;
+@end
+
+@implementation GradientView
+@synthesize direction = _direction;
+
++ (Class)layerClass {
+  return [CAGradientLayer class];
+}
+
+- (void)setDirection:(GradientViewDirection)direction {
+  _direction = direction;
+
+  CAGradientLayer* layer = static_cast<CAGradientLayer*>(self.layer);
+  layer.colors = @[
+    static_cast<id>([[UIColor clearColor] CGColor]),
+    static_cast<id>([[UIColor blackColor] CGColor])
+  ];
+
+  if (direction == GRADIENT_LEFT_TO_RIGHT) {
+    layer.transform = CATransform3DMakeRotation(M_PI_2, 0, 0, 1);
+  } else {
+    layer.transform = CATransform3DMakeRotation(-M_PI_2, 0, 0, 1);
+  }
+
+  [self setNeedsDisplay];
+}
+
+@end
+
+#pragma mark - ClippingMaskView
+
+@interface ClippingMaskView ()
+// The left gradient view.
+@property(nonatomic, strong) GradientView* leftGradientView;
+// The right gradient view.
+@property(nonatomic, strong) GradientView* rightGradientView;
+// The middle view. Used to paint everything not covered by the gradients with
+// opaque color.
+@property(nonatomic, strong) UIView* middleView;
+@end
+
+@implementation ClippingMaskView
+@synthesize fadeLeft = _fadeLeft;
+@synthesize fadeRight = _fadeRight;
+@synthesize middleView = _middleView;
+@synthesize leftGradientView = _leftGradientView;
+@synthesize rightGradientView = _rightGradientView;
+
+- (instancetype)initWithFrame:(CGRect)frame {
+  self = [super initWithFrame:frame];
+  if (self) {
+    _leftGradientView = [[GradientView alloc] init];
+    [_leftGradientView setTranslatesAutoresizingMaskIntoConstraints:NO];
+    _leftGradientView.direction = GRADIENT_RIGHT_TO_LEFT;
+
+    _rightGradientView = [[GradientView alloc] init];
+    [_rightGradientView setTranslatesAutoresizingMaskIntoConstraints:NO];
+    _rightGradientView.direction = GRADIENT_LEFT_TO_RIGHT;
+
+    _middleView = [[UIView alloc] init];
+    [_middleView setTranslatesAutoresizingMaskIntoConstraints:NO];
+    _middleView.backgroundColor = [UIColor blackColor];
+
+    [self addSubview:_leftGradientView];
+    [self addSubview:_middleView];
+    [self addSubview:_rightGradientView];
+  }
+  return self;
+}
+
+- (void)setFadeLeft:(BOOL)fadeLeft {
+  _fadeLeft = fadeLeft;
+  self.leftGradientView.hidden = !fadeLeft;
+  [self setNeedsLayout];
+}
+
+- (void)setFadeRight:(BOOL)fadeRight {
+  _fadeRight = fadeRight;
+  self.rightGradientView.hidden = !fadeRight;
+  [self setNeedsLayout];
+}
+
+// Since this view is intended to be used as a maskView of another UIView, and
+// maskViews are not in the view hierarchy, autolayout is not supported.
+// Luckily, the desired layout is easy:
+// |[leftGradientView][middleView][rightGradientView]|,
+// where the grad views are sometimes hidden (and then the middle view is
+// extended to that side). The gradients' widths are equal to the height of this
+// view.
+- (void)layoutSubviews {
+  [super layoutSubviews];
+  CGFloat height = self.bounds.size.height;
+  CGFloat gradientWidth = height;
+  CGFloat xOffset = 0;
+  if (self.fadeLeft) {
+    self.leftGradientView.frame = CGRectMake(0, 0, gradientWidth, height);
+    xOffset += gradientWidth;
+  }
+
+  CGFloat midWidth = self.bounds.size.width - xOffset;
+  if (self.fadeRight) {
+    midWidth -= gradientWidth;
+  }
+
+  self.middleView.frame = CGRectMake(xOffset, 0, midWidth, height);
+  xOffset += midWidth;
+
+  if (self.fadeRight) {
+    self.rightGradientView.frame =
+        CGRectMake(xOffset, 0, gradientWidth, height);
+  }
+}
+
+@end

ios/chrome/browser/ui/omnibox/clipping_textfield.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_H_
+#define IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_H_
+
+#import <UIKit/UIKit.h>
+
+@protocol ClippingTextFieldDelegate;
+
+// This textfield subclass is designed to be paired with
+// ClippingTextFieldContainer. It notifies its delegate about changes of text
+// and becoming/resigning first responder.
+@interface ClippingTextField : UITextField
+
+@property(nonatomic, weak) id<ClippingTextFieldDelegate>
+    clippingTextfieldDelegate;
+
+@end
+
+@protocol ClippingTextFieldDelegate
+
+// Called when setText: or setAttributedText: was called. Not called when the
+// textfield is being typed into.
+- (void)textFieldTextChanged:(UITextField*)sender;
+- (void)textFieldBecameFirstResponder:(UITextField*)sender;
+- (void)textFieldResignedFirstResponder:(UITextField*)sender;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_H_

ios/chrome/browser/ui/omnibox/clipping_textfield.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation ClippingTextField
+@synthesize clippingTextfieldDelegate = _clippingTextfieldDelegate;
+
+- (void)setText:(NSString*)setText {
+  [super setText:setText];
+  [self.clippingTextfieldDelegate textFieldTextChanged:self];
+}
+
+- (void)setAttributedText:(NSAttributedString*)attributedText {
+  [super setAttributedText:attributedText];
+  [self.clippingTextfieldDelegate textFieldTextChanged:self];
+}
+
+- (BOOL)becomeFirstResponder {
+  BOOL didBecomeFirstResponder = [super becomeFirstResponder];
+  [self.clippingTextfieldDelegate textFieldBecameFirstResponder:self];
+  return didBecomeFirstResponder;
+}
+
+- (BOOL)resignFirstResponder {
+  BOOL didResignFirstResponder = [super resignFirstResponder];
+  if (didResignFirstResponder) {
+    [self.clippingTextfieldDelegate textFieldResignedFirstResponder:self];
+  }
+  return didResignFirstResponder;
+}
+
+@end

ios/chrome/browser/ui/omnibox/clipping_textfield_container.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_CONTAINER_H_
+#define IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_CONTAINER_H_
+
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield.h"
+
+// A container for the textfield that manages clipping it appropriately.
+// It will size the textfield to fit precisely when the textfield is first
+// responder. Otherwise, it will clip the textfield to its own bounds in the
+// best way to fit the most significant part of the URL, like this:
+//
+//                     --------------------
+// www.somereallyreally|longdomainname.com|/path/gets/clipped
+//                     --------------------
+// {  clipped prefix  } {  visible text  } { clipped suffix }
+//
+// The clipped parts will also be masked with a gradient fade effect on the
+// clipped ends.
+@interface ClippingTextFieldContainer : UIView<ClippingTextFieldDelegate>
+
+// The only available initializer. This will immediately add |textField| as its
+// subview and set |self| as textField's clipping delegate.
+- (instancetype)initWithClippingTextField:(ClippingTextField*)textField
+    NS_DESIGNATED_INITIALIZER;
+
+- (instancetype)initWithFrame:(CGRect)frame NS_UNAVAILABLE;
+- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
+
+// Managed textfield.
+@property(nonatomic, strong, readonly) ClippingTextField* textField;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_OMNIBOX_CLIPPING_TEXTFIELD_CONTAINER_H_

ios/chrome/browser/ui/omnibox/clipping_textfield_container.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield_container.h"
+
+#include "base/strings/sys_string_conversions.h"
+#include "components/omnibox/browser/autocomplete_input.h"
+#include "ios/chrome/browser/autocomplete/autocomplete_scheme_classifier_impl.h"
+#import "ios/chrome/browser/ui/omnibox/clipping_mask_view.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@interface ClippingTextFieldContainer ()
+
+@property(nonatomic, strong) NSLayoutConstraint* leftConstraint;
+@property(nonatomic, strong) NSLayoutConstraint* rightConstraint;
+@property(nonatomic, strong) ClippingMaskView* gradientMaskView;
+@property(nonatomic, assign, getter=isClipping) BOOL clipping;
+
+@end
+
+@implementation ClippingTextFieldContainer
+@synthesize textField = _textField;
+@synthesize leftConstraint = _leftConstraint;
+@synthesize rightConstraint = _rightConstraint;
+@synthesize gradientMaskView = _gradientMaskView;
+@synthesize clipping = _clipping;
+
+- (instancetype)initWithClippingTextField:(ClippingTextField*)textField {
+  self = [super initWithFrame:CGRectZero];
+  if (self) {
+    _textField = textField;
+    textField.clippingTextfieldDelegate = self;
+    [self addSubview:textField];
+
+    _gradientMaskView = [[ClippingMaskView alloc] init];
+    self.maskView = _gradientMaskView;
+
+    // Configure layout.
+    // Left and Right are used instead of Leading and Trailing because the
+    // clipping only ever applies to URLs that are always displayed in LTR.
+    _leftConstraint =
+        [self.textField.leftAnchor constraintEqualToAnchor:self.leftAnchor];
+    _rightConstraint =
+        [self.textField.rightAnchor constraintEqualToAnchor:self.rightAnchor];
+    [NSLayoutConstraint activateConstraints:@[
+      [textField.topAnchor constraintEqualToAnchor:self.topAnchor],
+      [textField.bottomAnchor constraintEqualToAnchor:self.bottomAnchor],
+      _leftConstraint,
+      _rightConstraint,
+    ]];
+    textField.translatesAutoresizingMaskIntoConstraints = NO;
+    self.clipsToBounds = YES;
+    _clipping = NO;
+  }
+  return self;
+}
+
+- (void)layoutSubviews {
+  if ([self isClipping]) {
+    [self applyClipping];
+  }
+  [super layoutSubviews];
+  self.gradientMaskView.frame = self.bounds;
+}
+
+- (void)startClipping {
+  self.clipping = YES;
+  [self applyClipping];
+  [self setNeedsLayout];
+  [self layoutIfNeeded];
+}
+
+- (void)applyClipping {
+  CGFloat suffixWidth = 0;
+  CGFloat prefixWidth =
+      -[self leftConstantWithAttributedText:self.textField.attributedText
+                              rightConstant:&suffixWidth];
+
+  [self applyGradientsToPrefix:(prefixWidth < 0) suffix:(suffixWidth > 0)];
+
+  self.leftConstraint.constant = prefixWidth;
+  self.rightConstraint.constant = suffixWidth;
+}
+
+- (void)stopClipping {
+  if (![self isClipping]) {
+    return;
+  }
+  self.clipping = NO;
+  self.leftConstraint.constant = 0;
+  self.rightConstraint.constant = 0;
+  [self removeGradient];
+}
+
+// Fade the beginning and/or end of the visible string to indicate to the user
+// that the URL has been clipped.
+- (void)applyGradientsToPrefix:(BOOL)shouldApplyToPrefix
+                        suffix:(BOOL)shouldApplyToSuffix {
+  self.gradientMaskView.fadeLeft = shouldApplyToPrefix;
+  self.gradientMaskView.fadeRight = shouldApplyToSuffix;
+}
+
+- (void)removeGradient {
+  [self applyGradientsToPrefix:NO suffix:NO];
+}
+
+#pragma mark calculate clipping
+
+// Calculates the length (in pts) of the clipped text on the left and
+// right sides of the omnibox in order to show the most significant part of
+// the hostname.
+- (CGFloat)leftConstantWithAttributedText:(NSAttributedString*)attributedText
+                            rightConstant:(out CGFloat*)right {
+  // The goal is to always show the most significant part of the hostname
+  // (i.e. the end of the TLD).
+  //
+  //                     --------------------
+  // www.somereallyreally|longdomainname.com|/path/gets/clipped
+  //                     --------------------
+  // {  clipped prefix  } {  visible text  } { clipped suffix }
+
+  // First find how much (if any) of the scheme/host needs to be clipped so that
+  // the end of the TLD fits in bounds.
+
+  CGFloat widthOfClippedPrefix = 0;
+  url::Component scheme, host;
+  AutocompleteInput::ParseForEmphasizeComponents(
+      base::SysNSStringToUTF16(attributedText.string),
+      AutocompleteSchemeClassifierImpl(), &scheme, &host);
+  if (host.len < 0) {
+    return 0;
+  }
+  NSRange hostRange = NSMakeRange(0, host.begin + host.len);
+  NSAttributedString* hostString =
+      [attributedText attributedSubstringFromRange:hostRange];
+  CGFloat widthOfHost = ceil(hostString.size.width);
+  widthOfClippedPrefix = MAX(widthOfHost - self.bounds.size.width, 0);
+
+  // Now determine if there is any text that will need to be truncated because
+  // there's not enough room.
+  int textWidth = ceil(attributedText.size.width);
+  CGFloat widthOfClippedSuffix =
+      MAX(textWidth - self.bounds.size.width - widthOfClippedPrefix, 0);
+  *right = widthOfClippedSuffix;
+  return widthOfClippedPrefix;
+}
+
+#pragma mark - ClippingTextFieldDelegate
+
+- (void)textFieldTextChanged:(UITextField*)sender {
+  [self startClipping];
+}
+
+- (void)textFieldBecameFirstResponder:(UITextField*)sender {
+  [self stopClipping];
+}
+
+- (void)textFieldResignedFirstResponder:(UITextField*)sender {
+  [self startClipping];
+}
+
+@end

ios/chrome/browser/ui/omnibox/clipping_textfield_container_unittest.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield_container.h"
+
+#include "testing/platform_test.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+
+class ClippingTextFieldContainerTest : public PlatformTest {
+ protected:
+  void SetUp() override {
+    PlatformTest::SetUp();
+    textField_ = [[ClippingTextField alloc] init];
+    container_ = [[ClippingTextFieldContainer alloc]
+        initWithClippingTextField:textField_];
+
+    [[[UIApplication sharedApplication] keyWindow] addSubview:container_];
+    // Width of 200 is enough to fit "http://www.google.com" and is
+    // in the same ballpark as iPhone omnibox.
+    container_.frame = CGRectMake(0, 0, 200, 20);
+  };
+
+  void TearDown() override { [container_ removeFromSuperview]; }
+
+  ClippingTextFieldContainer* container_;
+  ClippingTextField* textField_;
+
+  UIView* LeftDecorationView() {
+    // The decoration container contains the decoration views covering the
+    // tail and the head.
+    UIView* decorationContainer = container_.maskView;
+    CGPoint leftMidPoint = CGPointMake(0, container_.bounds.size.height / 2);
+    for (UIView* decorationView in decorationContainer.subviews) {
+      if (CGRectContainsPoint(decorationView.frame, leftMidPoint) &&
+          [decorationView.layer class] == [CAGradientLayer class]) {
+        return decorationView;
+      }
+    }
+    return nil;
+  }
+
+  UIView* RightDecorationView() {
+    // The decoration container contains the decoration views covering the
+    // tail and the head.
+    UIView* decorationContainer = container_.maskView;
+    // Substract 0.5pt from x coordinate because CGRectContainsPoint
+    // returns NO for points on the maximum X edge.
+    CGPoint rightMidPoint = CGPointMake(container_.bounds.size.width - 0.5,
+                                        container_.bounds.size.height / 2);
+    for (UIView* decorationView in decorationContainer.subviews) {
+      if (CGRectContainsPoint(decorationView.frame, rightMidPoint) &&
+          [decorationView.layer class] == [CAGradientLayer class]) {
+        return decorationView;
+      }
+    }
+    return nil;
+  }
+};
+
+TEST_F(ClippingTextFieldContainerTest, DoesntClipWhenEntireURLFits) {
+  NSString* text = @"http://www.google.com";
+  [textField_ setText:text];
+
+  // The textfield fits in the container.
+  EXPECT_LE(textField_.frame.size.width, container_.frame.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, ClipsLongPrefix) {
+  NSString* text = @"http://verylongprefixwaymorethan200pts.google.com";
+  [textField_ setText:text];
+
+  // The left edge is clipped, so the textfield is shifted left.
+  EXPECT_TRUE(textField_.frame.origin.x < 0);
+  // The amount it's shifted left by is just enough to fit the URL.
+  EXPECT_EQ(textField_.frame.origin.x + textField_.frame.size.width,
+            container_.frame.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, ClipsLongSuffix) {
+  NSString* text = @"http://www.google.com/verylongsuffixwaymorethan200pts";
+  [textField_ setText:text];
+
+  // The left edge is not clipped.
+  EXPECT_EQ(textField_.frame.origin.x, 0);
+  // The right edge is clipped.
+  EXPECT_GE(textField_.frame.size.width, container_.frame.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, ClipsPrefixAndSuffix) {
+  NSString* text =
+      @"http://verylongprefixwaymorethan200pts.google.com/"
+      @"verylongsuffixwaymorethan200pts";
+  [textField_ setText:text];
+  CGSize textSize = [[textField_ attributedText] size];
+
+  // The left edge is clipped.
+  EXPECT_TRUE(textField_.frame.origin.x < 0);
+  // The right edge is clipped.
+  EXPECT_GE(textField_.frame.size.width + textField_.frame.origin.x,
+            container_.frame.size.width);
+  // The textfield expands to fit the text.
+  EXPECT_EQ(textField_.frame.size.width, ceil(textSize.width));
+}
+
+TEST_F(ClippingTextFieldContainerTest, NoScheme) {
+  NSString* text = @"www.google.com";
+  [textField_ setText:text];
+
+  // The textfield fits in the container.
+  EXPECT_LE(textField_.frame.size.width, container_.frame.size.width);
+  // The left edge is not clipped.
+  EXPECT_EQ(textField_.frame.origin.x, 0);
+
+  // Textfield's size is equal to container size and greater than text.
+  CGSize textSize = [[textField_ attributedText] size];
+  textSize.width = ceil(textSize.width);
+  textSize.height = ceil(textSize.height);
+  EXPECT_EQ(textField_.frame.size.width, container_.bounds.size.width);
+  EXPECT_LE(textSize.width, textField_.bounds.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, NoHost) {
+  NSString* text = @"http://";
+  [textField_ setText:text];
+
+  // The textfield fits in the container.
+  EXPECT_LE(textField_.frame.size.width, container_.frame.size.width);
+  // The left edge is not clipped.
+  EXPECT_EQ(textField_.frame.origin.x, 0);
+
+  // Textfield's size is equal to container size and greater than text.
+  CGSize textSize = [[textField_ attributedText] size];
+  textSize.width = ceil(textSize.width);
+  textSize.height = ceil(textSize.height);
+  EXPECT_EQ(textField_.frame.size.width, container_.bounds.size.width);
+  EXPECT_LE(textSize.width, textField_.bounds.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, DoesntClipWhenFocused) {
+  NSString* text =
+      @"http://verylongprefixwaymorethan200pts.google.com/"
+      @"verylongsuffixwaymorethan200pts";
+  [textField_ setText:text];
+
+  // The left edge is clipped.
+  EXPECT_TRUE(textField_.frame.origin.x < 0);
+  // The right edge is clipped.
+  EXPECT_GE(textField_.frame.size.width + textField_.frame.origin.x,
+            container_.frame.size.width);
+
+  [textField_ becomeFirstResponder];
+  [container_ layoutIfNeeded];
+
+  // When focused, the textfield should take the container's space and
+  // not be clipped.
+  EXPECT_EQ(textField_.frame.origin.x, 0);
+  EXPECT_EQ(textField_.frame.size.width, container_.frame.size.width);
+
+  [textField_ resignFirstResponder];
+  [container_ layoutIfNeeded];
+
+  // The left edge is clipped.
+  EXPECT_TRUE(textField_.frame.origin.x < 0);
+  // The right edge is clipped.
+  EXPECT_GE(textField_.frame.size.width + textField_.frame.origin.x,
+            container_.frame.size.width);
+}
+
+TEST_F(ClippingTextFieldContainerTest, ShowsDecorationsWhenClipping) {
+  NSString* text =
+      @"http://verylongprefixwaymorethan200pts.google.com/"
+      @"verylongsuffixwaymorethan200pts";
+  [textField_ setText:text];
+
+  // Tail and head are masked when the ends are clipped.
+  EXPECT_FALSE(LeftDecorationView().hidden);
+  EXPECT_FALSE(RightDecorationView().hidden);
+
+  [textField_ becomeFirstResponder];
+  [container_ layoutIfNeeded];
+
+  // Even for long strings, the masks are disabled while editing.
+  EXPECT_TRUE(LeftDecorationView().hidden);
+  EXPECT_TRUE(RightDecorationView().hidden);
+
+  [textField_ resignFirstResponder];
+  [container_ layoutIfNeeded];
+
+  // Deselecting textfield with a long string remasks the ends.
+  EXPECT_FALSE(LeftDecorationView().hidden);
+  EXPECT_FALSE(RightDecorationView().hidden);
+}
+
+}  // namespace

ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_CLIPPING_FEATURE_H_
+#define IOS_CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_CLIPPING_FEATURE_H_
+
+#include "base/feature_list.h"
+
+// Feature to choose whether to use the iOS 11-compatible textfield clipping.
+extern const base::Feature kClippingTextfield;
+
+#endif  // IOS_CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_CLIPPING_FEATURE_H_

ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h"
+
+const base::Feature kClippingTextfield{"kClippingTextfield",
+                                       base::FEATURE_ENABLED_BY_DEFAULT};

ios/chrome/browser/ui/omnibox/omnibox_text_field_ios.h

@@ -5,7 +5,7 @@
 #ifndef IOS_CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_TEXT_FIELD_IOS_H_
 #define IOS_CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_TEXT_FIELD_IOS_H_
 
-#import <UIKit/UIKit.h>
+#import "ios/chrome/browser/ui/omnibox/clipping_textfield.h"
 
 #include "base/strings/string16.h"
 #import "ios/chrome/browser/ui/omnibox/omnibox_text_field_delegate.h"
@@ -17,7 +17,7 @@ typedef enum {
 } OmniboxTextFieldFadeStyle;
 
 // UITextField subclass to allow for adjusting borders.
-@interface OmniboxTextFieldIOS : UITextField
+@interface OmniboxTextFieldIOS : ClippingTextField
 
 // Initialize the omnibox with the given frame, font, text color, and tint
 // color.

ios/chrome/browser/ui/omnibox/omnibox_text_field_ios.mm

@@ -18,6 +18,7 @@
 #include "ios/chrome/browser/autocomplete/autocomplete_scheme_classifier_impl.h"
 #include "ios/chrome/browser/experimental_flags.h"
 #import "ios/chrome/browser/ui/animation_util.h"
+#import "ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h"
 #include "ios/chrome/browser/ui/omnibox/omnibox_util.h"
 #import "ios/chrome/browser/ui/reversed_animation.h"
 #include "ios/chrome/browser/ui/rtl_geometry.h"
@@ -533,6 +534,12 @@ NSString* const kOmniboxFadeAnimationKey = @"OmniboxFadeAnimation";
 
 // Enumerate url components (host, path) and draw each one in different rect.
 - (void)drawTextInRect:(CGRect)rect {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // With the new clipping logic, this override is unnecessary.
+    [super drawTextInRect:rect];
+    return;
+  }
+
   if (base::ios::IsRunningOnOrLater(11, 1, 0)) {
     // -[UITextField drawTextInRect:] ignores the argument, so we can't do
     // anything on 11.1 and up.
@@ -839,6 +846,11 @@ NSString* const kOmniboxFadeAnimationKey = @"OmniboxFadeAnimation";
 }
 
 - (CGRect)rectForDrawTextInRect:(CGRect)rect {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // With the new clipping logic, this override is unnecessary.
+    return rect;
+  }
+
   // The goal is to always show the most significant part of the hostname
   // (i.e. the end of the TLD).
   //

ios/chrome/browser/ui/omnibox/omnibox_text_field_ios_unittest.mm

@@ -11,6 +11,7 @@
 #include "base/strings/string_split.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/chrome/browser/chrome_paths.h"
+#import "ios/chrome/browser/ui/omnibox/omnibox_clipping_feature.h"
 #include "ios/chrome/grit/ios_strings.h"
 #include "testing/gtest_mac.h"
 #include "testing/platform_test.h"
@@ -143,6 +144,12 @@ TEST_F(OmniboxTextFieldTest, enterPreEditState_preEditTextAlignment_change) {
 }
 
 TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_entireURLFits) {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // This test is expected to not work with new text field clipping because
+    // the code to implement clipping will be removed.
+    return;
+  }
+
   NSString* text = @"http://www.google.com";
   [textfield_ setText:text];
   CGSize textSize = [[textfield_ attributedText] size];
@@ -154,6 +161,12 @@ TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_entireURLFits) {
 }
 
 TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_clippedPrefix) {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // This test is expected to not work with new text field clipping because
+    // the code to implement clipping will be removed.
+    return;
+  }
+
   NSString* text = @"http://www.google.com";
   [textfield_ setText:text];
   CGSize textSize = [[textfield_ attributedText] size];
@@ -168,6 +181,12 @@ TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_clippedPrefix) {
 }
 
 TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_clippedSuffix) {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // This test is expected to not work with new text field clipping because
+    // the code to implement clipping will be removed.
+    return;
+  }
+
   NSString* text = @"http://www.google.com/somelongpath";
   [textfield_ setText:text];
   CGSize textSize = [[textfield_ attributedText] size];
@@ -180,6 +199,12 @@ TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_clippedSuffix) {
 }
 
 TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_noScheme) {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // This test is expected to not work with new text field clipping because
+    // the code to implement clipping will be removed.
+    return;
+  }
+
   NSString* text = @"www.google.com";
   [textfield_ setText:text];
   CGSize textSize = [[textfield_ attributedText] size];
@@ -192,6 +217,12 @@ TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_noScheme) {
 // When the text doesn't contain a host the method bails early and returns
 // the |rect| passed in.
 TEST_F(OmniboxTextFieldTest, rectForDrawTextInRect_noHost) {
+  if (base::FeatureList::IsEnabled(kClippingTextfield)) {
+    // This test is expected to not work with new text field clipping because
+    // the code to implement clipping will be removed.
+    return;
+  }
+
   NSString* text = @"http://";
   [textfield_ setText:text];
   CGSize textSize = [[textfield_ attributedText] size];

ios/chrome/browser/ui/toolbar/web_toolbar_controller.mm

@@ -268,6 +268,9 @@ using ios::material::TimingFunction;
   _keyboardDelegate = [[ToolbarAssistiveKeyboardDelegateImpl alloc] init];
   _keyboardDelegate.dispatcher = dispatcher;
   _keyboardDelegate.omniboxTextField = _locationBarView.textField;
+  [_locationBarView
+      setContentCompressionResistancePriority:UILayoutPriorityDefaultLow
+                                      forAxis:UILayoutConstraintAxisHorizontal];
 
   // Disable default drop interactions on the omnibox.
   // TODO(crbug.com/739903): Handle drop events once Chrome iOS is built with

ios/chrome/browser/ui/webui/web_ui_egtest.mm

@@ -104,7 +104,7 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
 
   // Verify that the resulting page is chrome://terms.
   [[EarlGrey selectElementWithMatcher:WaitForOmniboxText("chrome://terms")]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
   const std::string kTermsText = "Google Chrome Terms of Service";
   [ChromeEarlGrey waitForWebViewContainingText:kTermsText];
 }
@@ -119,7 +119,7 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
 
   // Verify that the resulting page is chrome://version.
   [[EarlGrey selectElementWithMatcher:WaitForOmniboxText("chrome://version")]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
   [ChromeEarlGrey waitForWebViewContainingText:"The Chromium Authors"];
 
   // Tap the back button in the toolbar and verify that the resulting page is
@@ -127,7 +127,7 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
   [[EarlGrey selectElementWithMatcher:BackButton()] performAction:grey_tap()];
   [[EarlGrey
       selectElementWithMatcher:WaitForOmniboxText("chrome://chrome-urls")]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
   [ChromeEarlGrey waitForWebViewContainingText:"List of Chrome URLs"];
 }
 
@@ -144,14 +144,14 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
   // corresponds to the first URL chrome://version that was loaded.
   [[EarlGrey selectElementWithMatcher:BackButton()] performAction:grey_tap()];
   [[EarlGrey selectElementWithMatcher:WaitForOmniboxText("chrome://version")]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
 
   // Tap the forward button in the toolbar and verify that the resulting page's
   // URL corresponds the second URL chrome://flags that was loaded.
   [[EarlGrey selectElementWithMatcher:ForwardButton()]
       performAction:grey_tap()];
   [[EarlGrey selectElementWithMatcher:WaitForOmniboxText("chrome://flags")]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
 }
 
 // Tests that all URLs on chrome://chrome-urls page load without error.
@@ -170,7 +170,7 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
     const std::string chrome_url_path =
         url::SchemeHostPort(kChromeUIScheme, kChromeHostURLs[i], 0).Serialize();
     [[EarlGrey selectElementWithMatcher:WaitForOmniboxText(chrome_url_path)]
-        assertWithMatcher:grey_sufficientlyVisible()];
+        assertWithMatcher:grey_notNil()];
   }
 }
 
@@ -182,7 +182,7 @@ id<GREYMatcher> WaitForOmniboxText(std::string text) {
 
   // Verify that the resulting page is an error page.
   [[EarlGrey selectElementWithMatcher:WaitForOmniboxText(kChromeInvalidURL)]
-      assertWithMatcher:grey_sufficientlyVisible()];
+      assertWithMatcher:grey_notNil()];
   NSString* kError =
       l10n_util::GetNSString(IDS_ERRORPAGES_HEADING_NOT_AVAILABLE);
   id<GREYMatcher> messageMatcher = [GREYMatchers matcherForText:kError];