Find root scroll layer at tree activation

cc/top_controls_manager.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/top_controls_manager.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/time.h"
@@ skipping 122 matching lines @@
     StartAnimationIfNecessary();
   }
 }
 
 void TopControlsManager::ResetAnimations() {
   if (top_controls_animation_)
     top_controls_animation_.reset();
 }
 
 LayerImpl* TopControlsManager::RootScrollLayer() {
-  return client_->activeTree()->root_scroll_layer();
+  return client_->rootScrollLayer();
 }
 
 float TopControlsManager::RootScrollLayerTotalScrollY() {
   LayerImpl* layer = RootScrollLayer();
   if (!layer)
     return 0;
   gfx::Vector2dF scroll_total = layer->scrollOffset() + layer->scrollDelta();
   return scroll_total.y();
 }
 
@@ skipping 17 matching lines @@
 
   if (controls_top_offset_ != 0
       && controls_top_offset_ != -top_controls_height_) {
     SetupAnimation(
         controls_top_offset_ >= -(top_controls_height_ * kShowHideThreshold));
     client_->setNeedsRedraw();
   }
 }
 
 }  // namespace cc