Adding UMA on page load size for pages with Media

chrome/browser/page_load_metrics/metrics_web_contents_observer.h

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.h
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
index 681e7cef03bfbe9b9fedf0c70416a535b9e503f9..a725db2b5c8a210e3f83313baea294bd166a063d 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
@@ -65,6 +65,9 @@ class MetricsWebContentsObserver
   void RenderProcessGone(base::TerminationStatus status) override;
   void RenderViewHostChanged(content::RenderViewHost* old_host,
                              content::RenderViewHost* new_host) override;
+  void MediaStartedPlaying(
+      const content::WebContentsObserver::MediaPlayerInfo& video_type,
+      const content::WebContentsObserver::MediaPlayerId& id) override;
 
   // These methods are forwarded from the MetricsNavigationThrottle.
   void WillStartNavigationRequest(content::NavigationHandle* navigation_handle);