Add a pan gesture in the tabstrip to reveal the thumb strip.

- Change the tabstrip's background to clear to allow the thumb
strip to be seen from behind it during enter/exit animation.
- Add a pan gesture recognizer to reveal/hide the thumb strip by
dragging down/up the tabstrip.

Bug: 1094335
Change-Id: I193d848f4ba2aaf07202c6d986496c2ed4b708a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315884
Commit-Queue: Roberto Moura <mouraroberto@google.com>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799950}

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

@@ -50,6 +50,7 @@ source_set("tabs") {
     "//ios/chrome/browser/ui/elements",
     "//ios/chrome/browser/ui/fullscreen",
     "//ios/chrome/browser/ui/fullscreen:feature_flags",
+    "//ios/chrome/browser/ui/gestures",
     "//ios/chrome/browser/ui/image_util",
     "//ios/chrome/browser/ui/ntp:util",
     "//ios/chrome/browser/ui/open_in",

ios/chrome/browser/ui/tabs/tab_strip_controller.h

@@ -11,6 +11,7 @@
 
 @protocol PopupMenuLongPressDelegate;
 @protocol TabStripPresentation;
+@class ViewRevealingVerticalPanHandler;
 class Browser;
 
 // Controller class for the tabstrip.  Manages displaying tabs and keeping the
@@ -32,6 +33,9 @@ class Browser;
 // Used to check if the tabstrip is visible before starting an animation.
 @property(nonatomic, assign) id<TabStripPresentation> presentationProvider;
 
+// Pan gesture handler for the tab strip.
+@property(nonatomic, weak) ViewRevealingVerticalPanHandler* panGestureHandler;
+
 // Designated initializer, |dispatcher| is not retained.
 - (instancetype)initWithBrowser:(Browser*)browser
                           style:(TabStripStyle)style NS_DESIGNATED_INITIALIZER;

ios/chrome/browser/ui/tabs/tab_strip_controller.mm

@@ -35,6 +35,7 @@
 #include "ios/chrome/browser/ui/fullscreen/fullscreen_controller.h"
 #import "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
 #include "ios/chrome/browser/ui/fullscreen/scoped_fullscreen_disabler.h"
+#import "ios/chrome/browser/ui/gestures/view_revealing_vertical_pan_handler.h"
 #import "ios/chrome/browser/ui/ntp/ntp_util.h"
 #import "ios/chrome/browser/ui/popup_menu/public/popup_menu_long_press_delegate.h"
 #import "ios/chrome/browser/ui/tabs/requirements/tab_strip_constants.h"
@@ -120,6 +121,11 @@ const CGFloat kNewTabButtonBottomImageInset = -2.0;
 
 // Returns the background color.
 UIColor* BackgroundColor() {
+  if (base::FeatureList::IsEnabled(kExpandedTabStrip)) {
+    // The background needs to be clear to allow the thumb strip to be seen
+    // from behind the tab strip during the enter/exit thumb strip animation.
+    return UIColor.clearColor;
+  }
   return UIColor.blackColor;
 }
 
@@ -282,6 +288,9 @@ UIColor* BackgroundColor() {
 // Handler for URL drop interactions.
 @property(nonatomic, strong) URLDragDropHandler* dragDropHandler;
 
+// Pan gesture recognizer for the view revealing pan gesture handler.
+@property(nonatomic, weak) UIPanGestureRecognizer* panGestureRecognizer;
+
 // Initializes the tab array based on the the entries in the |_webStateList|'s.
 // Creates one TabView per Tab and adds it to the tabstrip.  A later call to
 // |-layoutTabs| is needed to properly place the tabs in the correct positions.
@@ -423,6 +432,7 @@ UIColor* BackgroundColor() {
 @synthesize longPressDelegate = _longPressDelegate;
 @synthesize presentationProvider = _presentationProvider;
 @synthesize animationWaitDuration = _animationWaitDuration;
+@synthesize panGestureHandler = _panGestureHandler;
 
 - (instancetype)initWithBrowser:(Browser*)browser style:(TabStripStyle)style {
   if ((self = [super init])) {
@@ -569,6 +579,20 @@ UIColor* BackgroundColor() {
   [self layoutTabStripSubviews];
 }
 
+- (void)setPanGestureHandler:
+    (ViewRevealingVerticalPanHandler*)panGestureHandler {
+  _panGestureHandler = panGestureHandler;
+  [self.view removeGestureRecognizer:self.panGestureRecognizer];
+
+  UIPanGestureRecognizer* panGestureRecognizer = [[UIPanGestureRecognizer alloc]
+      initWithTarget:panGestureHandler
+              action:@selector(handlePanGesture:)];
+  panGestureRecognizer.maximumNumberOfTouches = 1;
+  [self.view addGestureRecognizer:panGestureRecognizer];
+
+  self.panGestureRecognizer = panGestureRecognizer;
+}
+
 #pragma mark - Private
 
 - (void)initializeTabArray {

ios/chrome/browser/ui/tabs/tab_strip_legacy_coordinator.h

@@ -12,6 +12,7 @@
 
 @protocol PopupMenuLongPressDelegate;
 @protocol TabStripPresentation;
+@class ViewRevealingVerticalPanHandler;
 
 // A legacy coordinator that presents the public interface for the tablet tab
 // strip feature.
@@ -28,6 +29,10 @@
 // synchronize animations.
 @property(nonatomic, assign) NSTimeInterval animationWaitDuration;
 
+// Sets the pan gesture handler for the tab strip controller.
+- (void)setPanGestureHandler:
+    (ViewRevealingVerticalPanHandler*)panGestureHandler;
+
 // Hides or shows the TabStrip.
 - (void)hideTabStrip:(BOOL)hidden;
 

ios/chrome/browser/ui/tabs/tab_strip_legacy_coordinator.mm

@@ -57,6 +57,11 @@
   [self.tabStripController tabStripSizeDidChange];
 }
 
+- (void)setPanGestureHandler:
+    (ViewRevealingVerticalPanHandler*)panGestureHandler {
+  self.tabStripController.panGestureHandler = panGestureHandler;
+}
+
 #pragma mark - ChromeCoordinator
 
 - (void)start {