Ensure Layers have valid sequence numbers for PropertyTrees

cc/layers/layer.h

 // Copyright 2010 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.
 
 #ifndef CC_LAYERS_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 452 matching lines @@
   }
 
   virtual void RunMicroBenchmark(MicroBenchmark* benchmark);
 
   void Set3dSortingContextId(int id);
   int sorting_context_id() const { return sorting_context_id_; }
 
   void set_property_tree_sequence_number(int sequence_number) {
     property_tree_sequence_number_ = sequence_number;
   }
+  int property_tree_sequence_number() { return property_tree_sequence_number_; }
 
   void SetTransformTreeIndex(int index);
   int transform_tree_index() const;
 
   void SetClipTreeIndex(int index);
   int clip_tree_index() const;
 
   void SetEffectTreeIndex(int index);
   int effect_tree_index() const;
 
@@ skipping 308 matching lines @@
   std::vector<FrameTimingRequest> frame_timing_requests_;
   bool frame_timing_requests_dirty_;
   bool is_hidden_from_property_trees_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_