Set up the infrastructure for Extension event metrics.

chrome/browser/extensions/extension_webui_apitest.cc

Index: chrome/browser/extensions/extension_webui_apitest.cc
diff --git a/chrome/browser/extensions/extension_webui_apitest.cc b/chrome/browser/extensions/extension_webui_apitest.cc
index 66333ccb4b5cef9bd58e7d2e5cca7c6d2438e476..a5047fcdd4ab63619c72d20721b51a1723d2c364 100644
--- a/chrome/browser/extensions/extension_webui_apitest.cc
+++ b/chrome/browser/extensions/extension_webui_apitest.cc
@@ -155,8 +155,8 @@ IN_PROC_BROWSER_TEST_F(ExtensionWebUITest, OnMessage) {
   OnMessage::Info info;
   info.data = "hi";
   info.last_message = true;
-  EventRouter::Get(profile())->BroadcastEvent(make_scoped_ptr(
-      new Event(OnMessage::kEventName, OnMessage::Create(info))));
+  EventRouter::Get(profile())->BroadcastEvent(make_scoped_ptr(new Event(
+      events::UNKNOWN, OnMessage::kEventName, OnMessage::Create(info))));
 
   scoped_ptr<ExtensionTestMessageListener> listener(
       new ExtensionTestMessageListener(false));