cc: Damage layer on delegated scroll

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 "base/basictypes.h"
@@ skipping 2676 matching lines @@
 }
 
 void LayerTreeHostImpl::SetRootLayerScrollOffsetDelegate(
       LayerScrollOffsetDelegate* root_layer_scroll_offset_delegate) {
   root_layer_scroll_offset_delegate_ = root_layer_scroll_offset_delegate;
   active_tree_->SetRootLayerScrollOffsetDelegate(
       root_layer_scroll_offset_delegate_);
 }
 
 void LayerTreeHostImpl::OnRootLayerDelegatedScrollOffsetChanged() {
-  DCHECK(root_layer_scroll_offset_delegate_ != NULL);
+  DCHECK(root_layer_scroll_offset_delegate_);
   client_->SetNeedsCommitOnImplThread();
+  SetNeedsRedraw();
+  active_tree_->OnRootLayerDelegatedScrollOffsetChanged();
   active_tree_->set_needs_update_draw_properties();
 }
 
 void LayerTreeHostImpl::ClearCurrentlyScrollingLayer() {
   active_tree_->ClearCurrentlyScrollingLayer();
   did_lock_scrolling_layer_ = false;
   scroll_affects_scroll_handler_ = false;
   accumulated_root_overscroll_ = gfx::Vector2dF();
 }
 
@@ skipping 674 matching lines @@
 }
 
 void LayerTreeHostImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   std::vector<PictureLayerImpl*>::iterator it =
       std::find(picture_layers_.begin(), picture_layers_.end(), layer);
   DCHECK(it != picture_layers_.end());
   picture_layers_.erase(it);
 }
 
 }  // namespace cc