Prevent create ScrollbarAnimationController for Mac Overlay Scrollbar

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3723 matching lines @@
         active_tree_->root_layer_for_testing()->LayerTreeAsJson());
     base::JSONWriter::WriteWithOptions(
         *json, base::JSONWriter::OPTIONS_PRETTY_PRINT, &str);
   }
   return str;
 }
 
 void LayerTreeHostImpl::RegisterScrollbarAnimationController(
     ElementId scroll_element_id,
     float scrollbar_opacity) {
-  if (settings().scrollbar_animator == LayerTreeSettings::NO_ANIMATOR)

[aelias_OOO_until_Jul13, 2017/06/02 22:02:23]

Why is this removed?

[chaopeng, 2017/06/05 14:52:40]

Moved to LayerTreeImpl::RegisterScrollbar.

-    return;
   if (ScrollbarAnimationControllerForElementId(scroll_element_id))
     return;
 
   scrollbar_animation_controllers_[scroll_element_id] =
       active_tree_->CreateScrollbarAnimationController(scroll_element_id,
                                                        scrollbar_opacity);
 }
 
 void LayerTreeHostImpl::UnregisterScrollbarAnimationController(
     ElementId scroll_element_id) {
@@ skipping 533 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc