Add protobuf serialization to DisplayItemList

cc/playback/clip_path_display_item.h

Index: cc/playback/clip_path_display_item.h
diff --git a/cc/playback/clip_path_display_item.h b/cc/playback/clip_path_display_item.h
index 08581e29dd14350172e1067468947dd710c6c945..b677fc7495df3bc69bcc4ffb13df95aad1811f57 100644
--- a/cc/playback/clip_path_display_item.h
+++ b/cc/playback/clip_path_display_item.h
@@ -22,6 +22,8 @@ class CC_EXPORT ClipPathDisplayItem : public DisplayItem {
 
   void SetNew(const SkPath& path, SkRegion::Op clip_op, bool antialias);
 
+  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;
@@ -44,6 +46,8 @@ class CC_EXPORT EndClipPathDisplayItem : public DisplayItem {
     return make_scoped_ptr(new EndClipPathDisplayItem());
   }
 
+  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;