Disable overlay scrollbars in Blink when hidden by the compositor.

cc/input/scrollbar_animation_controller.cc

 // Copyright 2014 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.h"
 
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
 
 ScrollbarAnimationController::ScrollbarAnimationController(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
     base::TimeDelta delay_before_starting,
     base::TimeDelta resize_delay_before_starting)
     : client_(client),
+      scroll_layer_id_(scroll_layer_id),
       delay_before_starting_(delay_before_starting),
       resize_delay_before_starting_(resize_delay_before_starting),
       is_animating_(false),
-      scroll_layer_id_(scroll_layer_id),
       currently_scrolling_(false),
       scroll_gesture_has_scrolled_(false),
       weak_factory_(this) {}
 
 ScrollbarAnimationController::~ScrollbarAnimationController() {}
 
 bool ScrollbarAnimationController::Animate(base::TimeTicks now) {
   if (!is_animating_)
     return false;
 
@@ skipping 59 matching lines @@
 void ScrollbarAnimationController::StopAnimation() {
   delayed_scrollbar_fade_.Cancel();
   is_animating_ = false;
 }
 
 ScrollbarSet ScrollbarAnimationController::Scrollbars() const {
   return client_->ScrollbarsFor(scroll_layer_id_);
 }
 
 }  // namespace cc