Add FadeOut delay animation to MouseLeave

cc/input/scrollbar_animation_controller.cc

Index: cc/input/scrollbar_animation_controller.cc
diff --git a/cc/input/scrollbar_animation_controller.cc b/cc/input/scrollbar_animation_controller.cc
index 56bf9657369d914d506bcd9d8087b1686206e129..dd4b6dac8665b458fd053abf32de443bb13c4b6b 100644
--- a/cc/input/scrollbar_animation_controller.cc
+++ b/cc/input/scrollbar_animation_controller.cc
@@ -125,6 +125,11 @@ void ScrollbarAnimationController::DidMouseLeave() {
 
   vertical_controller_->DidMouseLeave();
   horizontal_controller_->DidMouseLeave();
+
+  if (ScrollbarsHidden() || Captured())
+    return;
+
+  PostDelayedAnimationTask(false);
 }
 
 void ScrollbarAnimationController::DidMouseMoveNear(