Refactor delegated scrolling in LayerImpl

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>
 
@@ skipping 3001 matching lines @@
     scroll_info->scrolls.push_back(scroll);
   }
 
   for (size_t i = 0; i < layer_impl->children().size(); ++i)
     CollectScrollDeltas(scroll_info, layer_impl->children()[i]);
 }
 
 scoped_ptr<ScrollAndScaleSet> LayerTreeHostImpl::ProcessScrollDeltas() {
   scoped_ptr<ScrollAndScaleSet> scroll_info(new ScrollAndScaleSet());
 
+  if (root_layer_scroll_offset_delegate_)
+    root_layer_scroll_offset_delegate_->SetBlockUpdates(true);
   CollectScrollDeltas(scroll_info.get(), active_tree_->root_layer());
+  if (root_layer_scroll_offset_delegate_)
+    root_layer_scroll_offset_delegate_->SetBlockUpdates(false);
+
+  active_tree_->UpdateScrollOffsetDelegateIfNeeded();
+
   scroll_info->page_scale_delta =
       active_tree_->page_scale_factor()->PullDeltaForMainThread();
   scroll_info->top_controls_delta =
       active_tree()->top_controls_shown_ratio()->PullDeltaForMainThread();
   scroll_info->elastic_overscroll_delta =
       active_tree_->elastic_overscroll()->PullDeltaForMainThread();
   scroll_info->swap_promises.swap(swap_promises_for_main_thread_scroll_update_);
 
   return scroll_info.Pass();
 }
@@ skipping 431 matching lines @@
   new_target.SetToMin(layer_impl->MaxScrollOffset());
 
   curve->UpdateTarget(
       animation->TrimTimeToCurrentIteration(CurrentBeginFrameArgs().frame_time)
           .InSecondsF(),
       new_target);
 
   return true;
 }
 }  // namespace cc