[ios] Add layout to create TabStrip CollectionViewController.

This CL adds a collection view layout class for creating the tabstrip
viewcontroller.

Bug: 1128249,1130488.
Change-Id: Ie9faa75720fb0da8de3174887af945a4ee945bf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2421648Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Nazerke Kalidolda <nazerke@google.com>
Cr-Commit-Position: refs/heads/master@{#811942}

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

@@ -23,6 +23,8 @@ source_set("tab_strip_ui") {
   sources = [
     "tab_strip_view_controller.h",
     "tab_strip_view_controller.mm",
+    "tab_strip_view_layout.h",
+    "tab_strip_view_layout.mm",
   ]
   deps = [
     "//ios/chrome/browser/browser_state",

ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.h

@@ -7,13 +7,20 @@
 
 #import <UIKit/UIKit.h>
 
-@protocol PopupMenuLongPressDelegate;
-
 // ViewController for the TabStrip. This ViewController is contained by
 // BrowserViewController. This TabStripViewController is responsible for
 // responding to the different updates in the tabstrip view.
 @interface TabStripViewController : UICollectionViewController
 
+- (instancetype)init NS_DESIGNATED_INITIALIZER;
+
+- (instancetype)initWithNibName:(NSString*)nibNameOrNil
+                         bundle:(NSBundle*)nibBundleOrNil NS_UNAVAILABLE;
+- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
+
+- (instancetype)initWithCollectionViewLayout:(UICollectionViewLayout*)layout
+    NS_UNAVAILABLE;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_VIEW_CONTROLLER_H_

ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.mm

@@ -4,10 +4,23 @@
 
 #import "ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.h"
 
+#import "ios/chrome/browser/ui/tab_strip/tab_strip_view_layout.h"
+
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation TabStripViewController
 
+- (instancetype)init {
+  TabStripViewLayout* layout = [[TabStripViewLayout alloc] init];
+  self = [super initWithCollectionViewLayout:layout];
+  return self;
+}
+
+- (void)viewDidLoad {
+  [super viewDidLoad];
+  self.view.translatesAutoresizingMaskIntoConstraints = NO;
+}
+
 @end

ios/chrome/browser/ui/tab_strip/tab_strip_view_layout.h

+// Copyright 2020 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_TAB_STRIP_TAB_STRIP_VIEW_LAYOUT_H_
+#define IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_VIEW_LAYOUT_H_
+
+#import <UIKit/UIKit.h>
+
+// Layout used for TabStripView. This layout makes sure the tabs collection
+// is pinned to the top of view and the sizes of the resizable tabs are
+// correct.
+@interface TabStripViewLayout : UICollectionViewLayout
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_VIEW_LAYOUT_H_

ios/chrome/browser/ui/tab_strip/tab_strip_view_layout.mm

+// Copyright 2020 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/tab_strip/tab_strip_view_layout.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+
+// Tab dimensions.
+const CGFloat kTabOverlapStacked = 32.0;
+const CGFloat kMinTabWidthStacked = 200.0;
+
+}  // namespace
+
+@implementation TabStripViewLayout
+
+- (CGSize)collectionViewContentSize {
+  UICollectionView* collection = self.collectionView;
+  NSInteger num = [collection numberOfItemsInSection:0];
+
+  CGFloat width = kMinTabWidthStacked * num;
+  width -= (num - 1) * kTabOverlapStacked;
+  width = MAX(width, collection.bounds.size.width);
+  return CGSizeMake(width, collection.bounds.size.height);
+}
+
+// Retrieves layout information for an item at the specified index path
+// with a corresponding cell.
+- (UICollectionViewLayoutAttributes*)layoutAttributesForItemAtIndexPath:
+    (NSIndexPath*)indexPath {
+  UICollectionView* collection = self.collectionView;
+  CGRect bounds = collection.bounds;
+
+  // Calculating tab's length size depending on the number of tabs.
+  CGFloat x = indexPath.row * kMinTabWidthStacked;
+  if (indexPath.row > 0) {
+    x -= (kTabOverlapStacked * indexPath.row);
+  }
+
+  x = MAX(x, bounds.origin.x);
+
+  UICollectionViewLayoutAttributes* attr = [UICollectionViewLayoutAttributes
+      layoutAttributesForCellWithIndexPath:indexPath];
+  attr.frame =
+      CGRectMake(x, bounds.origin.y, kMinTabWidthStacked, bounds.size.height);
+  return attr;
+}
+
+- (NSArray<UICollectionViewLayoutAttributes*>*)
+    layoutAttributesForElementsInRect:(CGRect)rect {
+  NSInteger count = [self.collectionView numberOfItemsInSection:0];
+
+  NSMutableArray* result =
+      [NSMutableArray arrayWithCapacity:CGRectGetWidth(rect) / 190];
+  CGFloat x = CGRectGetMinX(rect);
+  NSInteger i = 0;
+  while (x < CGRectGetMaxX(rect) && i < count) {
+    // Modifies Layout attributes.
+    UICollectionViewLayoutAttributes* attr = [self
+        layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForRow:i
+                                                              inSection:0]];
+    [result addObject:attr];
+    x = CGRectGetMaxX(attr.frame);
+    i++;
+  }
+  return result;
+}
+
+- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
+  return YES;
+}
+
+- (UICollectionViewLayoutAttributes*)
+    initialLayoutAttributesForAppearingItemAtIndexPath:
+        (NSIndexPath*)itemIndexPath {
+  UICollectionViewLayoutAttributes* attr =
+      [self layoutAttributesForItemAtIndexPath:itemIndexPath];
+  CGRect frame = attr.frame;
+  frame.origin.y = CGRectGetMaxY(frame);
+  attr.frame = frame;
+  return attr;
+}
+
+@end