Serialize DisplayListRecordingSource to protos.

cc/playback/display_item_list.cc

Index: cc/playback/display_item_list.cc
diff --git a/cc/playback/display_item_list.cc b/cc/playback/display_item_list.cc
index a1a9cdbfc569a99c65c9243bb4cd41cc05fa0525..3496da0681e10ff3ae1e0c13d4aaa331f6d4c031 100644
--- a/cc/playback/display_item_list.cc
+++ b/cc/playback/display_item_list.cc
@@ -67,6 +67,8 @@ scoped_refptr<DisplayItemList> DisplayItemList::CreateFromProto(
       item->FromProtobuf(item_proto);
   }
 
+  list->Finalize();
+
   return list;
 }
 
@@ -327,7 +329,6 @@ void DisplayItemList::GenerateDiscardableImagesMetadata() {
   DCHECK(!settings_.use_cached_picture || picture_);
   if (settings_.use_cached_picture && !picture_->willPlayBackBitmaps())
     return;
-
   // The cached picture is translated by -layer_rect_.origin during record,
   // so we need to offset that back in order to get right positioning for
   // images.