Adding UMA on page load size for pages with Media

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index c17e82e38f311363f16317409a654afc114abd60..5efcfbbc33604f2306233ee5a882307f7dd8bed6 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -104,6 +104,14 @@ void MetricsWebContentsObserver::RenderViewHostChanged(
   RegisterInputEventObserver(new_host);
 }
 
+void MetricsWebContentsObserver::MediaStartedPlaying(
+    const content::WebContentsObserver::MediaPlayerInfo& video_type,
+    const content::WebContentsObserver::MediaPlayerId& id) {
+  if (committed_load_)

[Bryan McQuade, 2017/03/15 01:59:46]

we should just make sure that the top-level frame matches the currently
committed main frame first, similar to what we do in OnTimingUpdated. something
like

if (id.first>GetRenderViewHost()->GetMainFrame() !=
          web_contents()->GetMainFrame()) {
  // received a media notification for a different frame.
  // this may happen in cases where media starts playing in a document
  // that was navigated away from. ignore it.
  return;
}

+    committed_load_->MediaStartedPlaying(
+        video_type, id.first == web_contents()->GetMainFrame());
+}
+
 bool MetricsWebContentsObserver::OnMessageReceived(
     const IPC::Message& message,
     content::RenderFrameHost* render_frame_host) {