Iframe/div MD scrollbars get idle when mouse leaves the nested elements.

cc/input/scrollbar_animation_controller_thinning.cc

 // Copyright 2013 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.
 
 #include "cc/input/scrollbar_animation_controller_thinning.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/time/time.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_impl_base.h"
@@ skipping 66 matching lines @@
   }
 }
 
 const base::TimeDelta& ScrollbarAnimationControllerThinning::Duration() {
   if (current_animating_property_ == OPACITY)
     return fade_duration_;
   else
     return thinning_duration_;
 }
 
-void ScrollbarAnimationControllerThinning::DidCaptureScrollbarBegin() {
-  if (opacity_ == 0.0f)
+void ScrollbarAnimationControllerThinning::DidMouseDown() {
+  if (!mouse_is_over_scrollbar_ || opacity_ == 0.0f)
     return;
+
   StopAnimation();
   captured_ = true;
   ApplyOpacity(1.f);
   ApplyThumbThicknessScale(1.f);
 }
 
-void ScrollbarAnimationControllerThinning::DidCaptureScrollbarEnd() {
-  if (opacity_ == 0.0f)
+void ScrollbarAnimationControllerThinning::DidMouseUp() {
+  if (!captured_ || opacity_ == 0.0f)
     return;
+
   captured_ = false;
   StopAnimation();
 
   if (!mouse_is_near_scrollbar_) {
     SetCurrentAnimatingProperty(THICKNESS);
     thickness_change_ = DECREASE;
     StartAnimation();
   } else {
     SetCurrentAnimatingProperty(OPACITY);
     PostDelayedAnimationTask(false);
   }
 }
 
-void ScrollbarAnimationControllerThinning::DidMouseMoveOffScrollbar() {
+void ScrollbarAnimationControllerThinning::DidMouseLeave() {
   if (!mouse_is_over_scrollbar_ && !mouse_is_near_scrollbar_)
     return;
 
   mouse_is_over_scrollbar_ = false;
   mouse_is_near_scrollbar_ = false;
 
   if (captured_ || opacity_ == 0.0f)
     return;
 
   thickness_change_ = DECREASE;
@@ skipping 108 matching lines @@
   if (current_animating_property_ == property)
     return;
 
   StopAnimation();
   current_animating_property_ = property;
   if (current_animating_property_ == THICKNESS)
     ApplyOpacity(1.f);
 }
 
 }  // namespace cc