Disable overlay scrollbars in Blink when hidden by the compositor.

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/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 ScrollbarSet ScrollbarsFor(int scroll_layer_id) const = 0;
+  virtual void SetScrollbarsHidden(int layer_id, bool hidden) = 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:
@@ skipping 19 matching lines @@
   virtual const base::TimeDelta& Duration() = 0;
 
   void StartAnimation();
   void StopAnimation();
   ScrollbarSet Scrollbars() const;
 
   ScrollbarAnimationControllerClient* client_;
 
   void PostDelayedAnimationTask(bool on_resize);
 
+  int scroll_layer_id_;

[aelias_OOO_until_Jul13, 2016/10/26 19:01:03]

Please leave this private and introduce a protected getter instead.

[bokan, 2016/10/27 20:56:46]

Done.

+
  private:
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
 
   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_