cc: Don't perform image analysis if the DisplayItemList has no images.

cc/layers/recording_source.cc

Index: cc/layers/recording_source.cc
diff --git a/cc/layers/recording_source.cc b/cc/layers/recording_source.cc
index 9b1efbd7137db580582c602a6cfdb04eb56dd8c0..4193cf114f1f53c774328266bb39b49f7f6e2a10 100644
--- a/cc/layers/recording_source.cc
+++ b/cc/layers/recording_source.cc
@@ -56,8 +56,6 @@ void RecordingSource::FinishDisplayItemListUpdate() {
   TRACE_EVENT0("cc", "RecordingSource::FinishDisplayItemListUpdate");
   DetermineIfSolidColor();
   display_list_->EmitTraceSnapshot();
-  if (generate_discardable_images_metadata_)

[vmpstr, 2017/04/25 17:43:40]

This is the only place this flag is used afaik. If we're not relying on it then
we should remove it.

[Khushal, 2017/04/25 18:18:10]

That was my plan. After rebasing on your patch.

-    display_list_->GenerateDiscardableImagesMetadata();
 }
 
 void RecordingSource::SetNeedsDisplayRect(const gfx::Rect& layer_rect) {