Add protobuf serialization to DisplayItemList

cc/playback/filter_display_item.h

Index: cc/playback/filter_display_item.h
diff --git a/cc/playback/filter_display_item.h b/cc/playback/filter_display_item.h
index d9714c07cdc64e9d7c49b80e7d7b9c6f88318e26..414623cc5582d5ed0f0c03acccebefbd8ca149d4 100644
--- a/cc/playback/filter_display_item.h
+++ b/cc/playback/filter_display_item.h
@@ -22,6 +22,8 @@ class CC_EXPORT FilterDisplayItem : public DisplayItem {
 
   void SetNew(const FilterOperations& filters, const gfx::RectF& bounds);
 
+  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;
@@ -43,6 +45,8 @@ class CC_EXPORT EndFilterDisplayItem : public DisplayItem {
     return make_scoped_ptr(new EndFilterDisplayItem());
   }
 
+  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;