Remove dom_loading from page_load_metrics

chrome/common/page_load_metrics/page_load_timing.h

Index: chrome/common/page_load_metrics/page_load_timing.h
diff --git a/chrome/common/page_load_metrics/page_load_timing.h b/chrome/common/page_load_metrics/page_load_timing.h
index fcb642da270b4f33d10778948d860462f37f85a3..e41235b49f8f8e6805307f3ba47ae4b5447b2443 100644
--- a/chrome/common/page_load_metrics/page_load_timing.h
+++ b/chrome/common/page_load_metrics/page_load_timing.h
@@ -35,10 +35,6 @@ struct PageLoadTiming {
   // Time that the first byte of the response is received.
   base::Optional<base::TimeDelta> response_start;
 
-  // Time that the document transitions to the 'loading' state. This is roughly
-  // the time that the HTML parser begins parsing the main HTML resource.
-  base::Optional<base::TimeDelta> dom_loading;
-
   // Time immediately before the DOMContentLoaded event is fired.
   base::Optional<base::TimeDelta> dom_content_loaded_event_start;