Overlay scrollbars shouldn't fade out while mouse is over/near.

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 54 matching lines @@
     ApplyOpacity(1.f - progress);
   else
     ApplyThumbThicknessScale(ThumbThicknessScaleAt(progress));
 
   client_->SetNeedsRedrawForScrollbarAnimation();
   if (progress == 1.f) {
     StopAnimation();
     if (current_animating_property_ == THICKNESS) {
       thickness_change_ = NONE;
       SetCurrentAnimatingProperty(OPACITY);
-      PostDelayedAnimationTask(false);
+      if (!mouse_is_near_scrollbar_) {

[aelias_OOO_until_Jul13, 2016/12/07 22:35:09]

nit: no braces for this in Chromium style

+        PostDelayedAnimationTask(false);
+      }
     }
   }
 }
 
 const base::TimeDelta& ScrollbarAnimationControllerThinning::Duration() {
   if (current_animating_property_ == OPACITY)
     return fade_duration_;
   else
     return thinning_duration_;
 }
@@ skipping 14 matching lines @@
 
   captured_ = false;
   StopAnimation();
 
   if (!mouse_is_near_scrollbar_) {
     SetCurrentAnimatingProperty(THICKNESS);
     thickness_change_ = DECREASE;
     StartAnimation();
   } else {
     SetCurrentAnimatingProperty(OPACITY);
-    PostDelayedAnimationTask(false);
   }
 }
 
 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;
   SetCurrentAnimatingProperty(THICKNESS);
   StartAnimation();
 }
 
 void ScrollbarAnimationControllerThinning::DidScrollUpdate(bool on_resize) {
   if (captured_)
     return;
 
   ScrollbarAnimationController::DidScrollUpdate(on_resize);
   ApplyOpacity(1.f);
   ApplyThumbThicknessScale(mouse_is_near_scrollbar_ ? 1.f
                                                     : kIdleThicknessScale);
   SetCurrentAnimatingProperty(OPACITY);
+
+  // Don't fade out the scrollbar when mouse is near.
+  if (mouse_is_near_scrollbar_)
+    StopAnimation();
+}
+
+void ScrollbarAnimationControllerThinning::DidScrollEnd() {
+  ScrollbarAnimationController::DidScrollEnd();
+
+  // Don't fade out the scrollbar when mouse is near.
+  if (mouse_is_near_scrollbar_)
+    StopAnimation();
 }
 
 void ScrollbarAnimationControllerThinning::DidMouseMoveNear(float distance) {
   bool mouse_is_over_scrollbar = distance == 0.0f;
   bool mouse_is_near_scrollbar =
       distance < mouse_move_distance_to_trigger_animation_;
 
   if (captured_ || opacity_ == 0.0f) {
     mouse_is_near_scrollbar_ = mouse_is_near_scrollbar;
     mouse_is_over_scrollbar_ = mouse_is_over_scrollbar;
@@ skipping 95 matching lines @@
   if (current_animating_property_ == property)
     return;
 
   StopAnimation();
   current_animating_property_ = property;
   if (current_animating_property_ == THICKNESS)
     ApplyOpacity(1.f);
 }
 
 }  // namespace cc