Prevent overlay scrollbars expand or hover together

cc/input/scrollbar_animation_controller.h

 // Copyright 2012 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 CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
+#include "cc/input/single_scrollbar_animation_controller_thinning.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_impl_base.h"
 #include "ui/gfx/geometry/vector2d_f.h"
 
 namespace cc {
 
-class ScrollbarAnimationController;
-
 class CC_EXPORT ScrollbarAnimationControllerClient {
  public:
   virtual void PostDelayedScrollbarAnimationTask(const base::Closure& task,
                                                  base::TimeDelta delay) = 0;
   virtual void SetNeedsRedrawForScrollbarAnimation() = 0;
   virtual void SetNeedsAnimateForScrollbarAnimation() = 0;
   virtual void DidChangeScrollbarVisibility() = 0;
   virtual ScrollbarSet ScrollbarsFor(int scroll_layer_id) const = 0;
 
  protected:
   virtual ~ScrollbarAnimationControllerClient() {}
 };
 
 // This abstract class represents the compositor-side analogy of
 // ScrollbarAnimator.  Individual platforms should subclass it to provide
 // specialized implementation.
+// This class also passes the mouse state to each
+// SingleScrollbarAnimationControllerThinning. The thinning animations are
+// independent between vertical/horizontal and are managed by the
+// SingleScrollbarAnimationControllerThinnings.
 class CC_EXPORT ScrollbarAnimationController {
  public:
   virtual ~ScrollbarAnimationController();
 
   bool Animate(base::TimeTicks now);
 
   virtual void DidScrollBegin();
   virtual void DidScrollUpdate(bool on_resize);
   virtual void DidScrollEnd();
-  virtual void DidMouseDown() {}
-  virtual void DidMouseUp() {}
-  virtual void DidMouseLeave() {}
-  virtual void DidMouseMoveNear(float distance) {}
   virtual bool ScrollbarsHidden() const;
+  virtual bool NeedThinningAnimation() const;

[weiliangc, 2017/01/26 23:13:54]

Not need to change this, just providing some alternative way to implement this:
could either do a const bool that is set during constructor, or only call Create
of SingleScrollbarAnimationControllerThinning in
ScrollbarAnimationControllerThinning constructor and check whether the pointers
are null whenever try to access.

+
+  void DidMouseDown();
+  void DidMouseUp();
+  void DidMouseLeave();
+  void DidMouseMoveNear(ScrollbarOrientation, float);
+
+  bool mouse_is_over_scrollbar(ScrollbarOrientation orientation) const;
+  bool mouse_is_near_scrollbar(ScrollbarOrientation orientation) const;
+  bool mouse_is_near_any_scrollbar() const;
+
+  void set_mouse_move_distance_for_test(float distance);
 
  protected:
   ScrollbarAnimationController(int scroll_layer_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta delay_before_starting,
                                base::TimeDelta resize_delay_before_starting);
 
   virtual void RunAnimationFrame(float progress) = 0;
   virtual const base::TimeDelta& Duration() = 0;
+  virtual void ApplyOpacityToScrollbars(float opacity) = 0;
 
   void StartAnimation();
   void StopAnimation();
   ScrollbarSet Scrollbars() const;
 
   ScrollbarAnimationControllerClient* client_;
 
   void PostDelayedAnimationTask(bool on_resize);
 
   int scroll_layer_id() const { return scroll_layer_id_; }
 
+  bool animating_fade() const { return is_animating_; }
+
+  bool Captured() const;
+
+  std::unique_ptr<SingleScrollbarAnimationControllerThinning>
+      vertical_controller_;
+  std::unique_ptr<SingleScrollbarAnimationControllerThinning>
+      horizontal_controller_;
+
  private:
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
 
+  SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
+      ScrollbarOrientation) const;
+
   base::TimeTicks last_awaken_time_;
   base::TimeDelta delay_before_starting_;
   base::TimeDelta resize_delay_before_starting_;
 
   bool is_animating_;
 
   int scroll_layer_id_;
   bool currently_scrolling_;
   bool scroll_gesture_has_scrolled_;
   base::CancelableClosure delayed_scrollbar_fade_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_