Fix check for changing SurfaceId.

cc/surfaces/compositor_frame_sink_support.cc

 // Copyright 2016 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/surfaces/compositor_frame_sink_support.h"
 
 #include <algorithm>
 #include <utility>
 #include <vector>
 
@@ skipping 140 matching lines @@
   surface_factory_.ClearSurface();
 }
 
 void CompositorFrameSinkSupport::ReferencedSurfacesChanged(
     const LocalSurfaceId& local_surface_id,
     const std::vector<SurfaceId>* active_referenced_surfaces,
     const std::vector<SurfaceId>* pending_referenced_surfaces) {
   if (!surface_manager_->using_surface_references())
     return;
 
+  SurfaceId last_surface_id = reference_tracker_.current_surface_id();
+
   // Populate list of surface references to add and remove based on reference
   // surfaces in current frame compared with the last frame. The list of
   // surface references includes references from both the pending and active
   // frame if any.
   reference_tracker_.UpdateReferences(local_surface_id,
                                       active_referenced_surfaces,
                                       pending_referenced_surfaces);
 
-  SurfaceId last_surface_id = reference_tracker_.current_surface_id();
   UpdateSurfaceReferences(last_surface_id, local_surface_id);
 }
 
 void CompositorFrameSinkSupport::ReturnResources(
     const ReturnedResourceArray& resources) {
   if (resources.empty())
     return;
 
   if (!ack_pending_count_ && client_) {
     client_->ReclaimResources(resources);
@@ skipping 48 matching lines @@
   else
     begin_frame_source_->RemoveObserver(this);
 }
 
 void CompositorFrameSinkSupport::RequestCopyOfSurface(
     std::unique_ptr<CopyOutputRequest> request) {
   surface_factory_.RequestCopyOfSurface(std::move(request));
 }
 
 }  // namespace cc