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

cc/input/scrollbar_animation_controller_thinning.cc

Index: cc/input/scrollbar_animation_controller_thinning.cc
diff --git a/cc/input/scrollbar_animation_controller_thinning.cc b/cc/input/scrollbar_animation_controller_thinning.cc
index 2006d98fddb44a0779c850a7be0c32edb12c5d1c..c13876e4bc7cd65188cb548d833366df54202106 100644
--- a/cc/input/scrollbar_animation_controller_thinning.cc
+++ b/cc/input/scrollbar_animation_controller_thinning.cc
@@ -72,7 +72,9 @@ void ScrollbarAnimationControllerThinning::RunAnimationFrame(float progress) {
     if (current_animating_property_ == THICKNESS) {
       thickness_change_ = NONE;
       SetCurrentAnimatingProperty(OPACITY);
-      PostDelayedAnimationTask(false);
+      if (!mouse_is_near_scrollbar_) {
+        PostDelayedAnimationTask(false);
+      }
     }
   }
 }
@@ -107,7 +109,6 @@ void ScrollbarAnimationControllerThinning::DidMouseUp() {
     StartAnimation();
   } else {
     SetCurrentAnimatingProperty(OPACITY);
-    PostDelayedAnimationTask(false);
   }
 }
 
@@ -135,6 +136,18 @@ void ScrollbarAnimationControllerThinning::DidScrollUpdate(bool on_resize) {
   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) {