cc: Add image to rect map in DiscardableImageMap.

cc/playback/raster_source.cc

Index: cc/playback/raster_source.cc
diff --git a/cc/playback/raster_source.cc b/cc/playback/raster_source.cc
index e108be37dc44742f9353c21e14395e42a16abb72..06b678856bd02c474cb3f89b1d942de93b8d4d87 100644
--- a/cc/playback/raster_source.cc
+++ b/cc/playback/raster_source.cc
@@ -247,6 +247,10 @@ void RasterSource::GetDiscardableImagesInRect(
   display_list_->GetDiscardableImagesInRect(layer_rect, contents_scale, images);
 }
 
+gfx::Rect RasterSource::GetRectForImage(ImageId image_id) const {
+  return display_list_->GetRectForImage(image_id);
+}
+
 bool RasterSource::CoversRect(const gfx::Rect& layer_rect) const {
   if (size_.IsEmpty())
     return false;