Disable overlay scrollbars in Blink when hidden by the compositor.

cc/input/scrollbar_animation_controller.h

Index: cc/input/scrollbar_animation_controller.h
diff --git a/cc/input/scrollbar_animation_controller.h b/cc/input/scrollbar_animation_controller.h
index 7bb421f4946bf9d18251f64fbf31c61cf084a050..9d6ab6a37f55e7509213c29cff4c4d0c66a61265 100644
--- a/cc/input/scrollbar_animation_controller.h
+++ b/cc/input/scrollbar_animation_controller.h
@@ -24,6 +24,7 @@ class CC_EXPORT ScrollbarAnimationControllerClient {
   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() {}
@@ -63,6 +64,8 @@ class CC_EXPORT ScrollbarAnimationController {
 
   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.
@@ -74,7 +77,6 @@ class CC_EXPORT ScrollbarAnimationController {
 
   bool is_animating_;
 
-  int scroll_layer_id_;
   bool currently_scrolling_;
   bool scroll_gesture_has_scrolled_;
   base::CancelableClosure delayed_scrollbar_fade_;