Add protobuf serialization to DisplayItemList

cc/playback/transform_display_item.h

Index: cc/playback/transform_display_item.h
diff --git a/cc/playback/transform_display_item.h b/cc/playback/transform_display_item.h
index 9d3f9c6da468c4d4eda4ed40cbb08560a3c83978..304ee8cc94924b0d5c5462387f4dbd47eb2f4055 100644
--- a/cc/playback/transform_display_item.h
+++ b/cc/playback/transform_display_item.h
@@ -21,6 +21,8 @@ class CC_EXPORT TransformDisplayItem : public DisplayItem {
 
   void SetNew(const gfx::Transform& transform);
 
+  void ToProtobuf(proto::DisplayItem* proto) const override;
+  void FromProtobuf(const proto::DisplayItem& proto) override;
   void Raster(SkCanvas* canvas,
               const gfx::Rect& canvas_target_playback_rect,
               SkPicture::AbortCallback* callback) const override;
@@ -39,6 +41,8 @@ class CC_EXPORT EndTransformDisplayItem : public DisplayItem {
     return make_scoped_ptr(new EndTransformDisplayItem());
   }
 
+  void ToProtobuf(proto::DisplayItem* proto) const override;
+  void FromProtobuf(const proto::DisplayItem& proto) override;
   void Raster(SkCanvas* canvas,
               const gfx::Rect& canvas_target_playback_rect,
               SkPicture::AbortCallback* callback) const override;