Adding previews information to PLM UKM

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 5d35bf3ebc7fc1ced60bdc9e4e6f185acbbdeae6..b54b71f93f8b365a4f266e9520caadeec7eeb75f 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
@@ -138,6 +138,11 @@ class MetricsWebContentsObserver
                        const mojom::PageLoadTiming& timing,
                        const mojom::PageLoadMetadata& metadata);
 
+  // Informs the observers of the currently committed load that the event
+  // corresponding to |event_key| has occurred. This should not be called within
+  // WebContentsObserver::DidFinishNavigation methods.
+  void BroadcastEventToObservers(const void* const event_key);

[Bryan McQuade, 2017/07/12 21:10:03]

let's add to the comment that this API is subject to change and may be removed
in the future - my hope is to get rid of this in favor for looking up observer
by type, but that'll take a bit more time.

[RyanSturm, 2017/07/12 21:27:27]

Done.

+
  private:
   friend class content::WebContentsUserData<MetricsWebContentsObserver>;