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 <vector>
+
 #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/scrollbar.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;
+using std::vector;
 
 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.
 class CC_EXPORT ScrollbarAnimationController {
  public:
+  struct DistanceToScrollbar {
+    ScrollbarOrientation orientation_;
+    float distance_;
+
+    DistanceToScrollbar(ScrollbarOrientation orientation, float distance)
+        : orientation_(orientation), distance_(distance) {}
+  };
   virtual ~ScrollbarAnimationController();
 
-  bool Animate(base::TimeTicks now);
+  virtual 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 void DidMouseMoveNear(vector<DistanceToScrollbar>) {}

[bokan, 2016/12/06 19:44:46]

Rather than introducing DistanceToScrollbar, I think using (Orientation,
distance) as params here is better. If you need to just make two calls at the
call site.

   virtual bool ScrollbarsHidden() const;
 
  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;
@@ skipping 23 matching lines @@
   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_