Add protobuf serialization to DisplayItemList

cc/playback/display_item.h

 // Copyright 2014 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_PLAYBACK_DISPLAY_ITEM_H_
 #define CC_PLAYBACK_DISPLAY_ITEM_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "cc/debug/traced_value.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "ui/gfx/geometry/rect.h"
 
 class SkCanvas;
 
 namespace cc {
 
+namespace proto {
+class DisplayItem;
+}
+
 class CC_EXPORT DisplayItem {
  public:
   virtual ~DisplayItem() {}
 
   void SetNew(bool is_suitable_for_gpu_rasterization,
               int approximate_op_count,
               size_t external_memory_usage) {
     is_suitable_for_gpu_rasterization_ = is_suitable_for_gpu_rasterization;
     approximate_op_count_ = approximate_op_count;
     external_memory_usage_ = external_memory_usage;
   }
 
+  virtual void ToProtobuf(proto::DisplayItem* proto) const = 0;
+  virtual void FromProtobuf(const proto::DisplayItem& proto) = 0;
   virtual void Raster(SkCanvas* canvas,
                       const gfx::Rect& canvas_target_playback_rect,
                       SkPicture::AbortCallback* callback) const = 0;
   virtual void AsValueInto(base::trace_event::TracedValue* array) const = 0;
 
   bool is_suitable_for_gpu_rasterization() const {
     return is_suitable_for_gpu_rasterization_;
   }
   int approximate_op_count() const { return approximate_op_count_; }
   size_t external_memory_usage() const { return external_memory_usage_; }
 
  protected:
   DisplayItem();
 
   bool is_suitable_for_gpu_rasterization_;
   int approximate_op_count_;
 
   // The size, in bytes, of the memory owned by this display item but not
   // allocated within it (e.g. held through scoped_ptr or vector).
   size_t external_memory_usage_;
 };
 
 }  // namespace cc
 
 #endif  // CC_PLAYBACK_DISPLAY_ITEM_H_