Plumb smooth scrolling in Chromium compositor

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 <algorithm>
 #include <limits>
 #include <map>
 #include <set>
@@ skipping 1848 matching lines @@
 
 LayerImpl* LayerTreeHostImpl::OuterViewportScrollLayer() const {
   return active_tree_->OuterViewportScrollLayer();
 }
 
 LayerImpl* LayerTreeHostImpl::CurrentlyScrollingLayer() const {
   return active_tree_->CurrentlyScrollingLayer();
 }
 
 bool LayerTreeHostImpl::IsActivelyScrolling() const {
-  return (did_lock_scrolling_layer_ && CurrentlyScrollingLayer()) ||
-         (InnerViewportScrollLayer() &&
-          InnerViewportScrollLayer()->IsExternalScrollActive()) ||
-         (OuterViewportScrollLayer() &&
-          OuterViewportScrollLayer()->IsExternalScrollActive());
+  return did_lock_scrolling_layer_ && CurrentlyScrollingLayer();
 }
 
 // Content layers can be either directly scrollable or contained in an outer
 // scrolling layer which applies the scroll transform. Given a content layer,
 // this function returns the associated scroll layer if any.
 static LayerImpl* FindScrollLayerForContentLayer(LayerImpl* layer_impl) {
   if (!layer_impl)
     return NULL;
 
   if (layer_impl->scrollable())
@@ skipping 1732 matching lines @@
   if (active_tree()) {
     LayerAnimationValueProvider* layer = active_tree()->LayerById(layer_id);
     if (layer)
       return layer->ScrollOffsetForAnimation();
   }
 
   return gfx::ScrollOffset();
 }
 
 }  // namespace cc