Add protobuf serialization to DisplayItemList

cc/playback/float_clip_display_item.h

Index: cc/playback/float_clip_display_item.h
diff --git a/cc/playback/float_clip_display_item.h b/cc/playback/float_clip_display_item.h
index 65449b886a8d373da22bc945d52bbe0d06c99043..2f68ee99da3746fd0bf9ddc6c0f3b885e68f2ecd 100644
--- a/cc/playback/float_clip_display_item.h
+++ b/cc/playback/float_clip_display_item.h
@@ -23,6 +23,8 @@ class CC_EXPORT FloatClipDisplayItem : public DisplayItem {
 
   void SetNew(const gfx::RectF& clip_rect);
 
+  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 EndFloatClipDisplayItem : public DisplayItem {
     return make_scoped_ptr(new EndFloatClipDisplayItem());
   }
 
+  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;