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 1bd69cca3f28fbd530d459f8d4ca30863577cc2b..5a8a5f9629d104bd9f30035f9b5e15334e57b742 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) override;
+  void FromProtobuf(const proto::DisplayItem& proto) override;
   void Raster(SkCanvas* canvas,
               const gfx::Rect& canvas_target_playback_rect,
               SkPicture::AbortCallback* callback) const override;
@@ -41,6 +43,8 @@ class CC_EXPORT EndTransformDisplayItem : public DisplayItem {
     return make_scoped_ptr(new EndTransformDisplayItem());
   }
 
+  void ToProtobuf(proto::DisplayItem* proto) override;
+  void FromProtobuf(const proto::DisplayItem& proto) override;
   void Raster(SkCanvas* canvas,
               const gfx::Rect& canvas_target_playback_rect,
               SkPicture::AbortCallback* callback) const override;