Set up the infrastructure for Extension event metrics.

chrome/browser/apps/ephemeral_app_browsertest.cc

Index: chrome/browser/apps/ephemeral_app_browsertest.cc
diff --git a/chrome/browser/apps/ephemeral_app_browsertest.cc b/chrome/browser/apps/ephemeral_app_browsertest.cc
index de35c13fde5b5ce6a4e49522908a1b42eb8b866c..f1682897ed92c1f20c5edbaae7c04f40dd93088d 100644
--- a/chrome/browser/apps/ephemeral_app_browsertest.cc
+++ b/chrome/browser/apps/ephemeral_app_browsertest.cc
@@ -426,8 +426,8 @@ class EphemeralAppBrowserTest : public EphemeralAppTestBase {
 
     scoped_ptr<base::ListValue> args(new base::ListValue());
     args->Append(dummy_alarm.ToValue().release());
-    scoped_ptr<Event> event(new Event(alarms::OnAlarm::kEventName,
-                                      args.Pass()));
+    scoped_ptr<Event> event(new Event(
+        extensions::events::UNKNOWN, alarms::OnAlarm::kEventName, args.Pass()));
 
     event_router->DispatchEventToExtension(app_id, event.Pass());
   }