Set up the infrastructure for Extension event metrics.

chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc

Index: chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc
diff --git a/chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc b/chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc
index f83858a094ade26f8d98fd01c97c1154c2c901fc..5543d8b7dabc0b71d024528e757be042919ba744 100644
--- a/chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc
+++ b/chrome/browser/extensions/api/tab_capture/tab_capture_registry.cc
@@ -313,8 +313,8 @@ void TabCaptureRegistry::DispatchStatusChangeEvent(
   tab_capture::CaptureInfo info;
   request->GetCaptureInfo(&info);
   args->Append(info.ToValue().release());
-  scoped_ptr<Event> event(new Event(tab_capture::OnStatusChanged::kEventName,
-      args.Pass()));
+  scoped_ptr<Event> event(new Event(
+      events::UNKNOWN, tab_capture::OnStatusChanged::kEventName, args.Pass()));
   event->restrict_to_browser_context = browser_context_;
 
   router->DispatchEventToExtension(request->extension_id(), event.Pass());