Set up the infrastructure for Extension event metrics.

extensions/browser/api/serial/serial_event_dispatcher.cc

Index: extensions/browser/api/serial/serial_event_dispatcher.cc
diff --git a/extensions/browser/api/serial/serial_event_dispatcher.cc b/extensions/browser/api/serial/serial_event_dispatcher.cc
index 930c1efe29446066ec68e84034ffaf19f6850615..97ab8ac9dc6f751ded743d51469eab3de354218f 100644
--- a/extensions/browser/api/serial/serial_event_dispatcher.cc
+++ b/extensions/browser/api/serial/serial_event_dispatcher.cc
@@ -99,7 +99,8 @@ void SerialEventDispatcher::ReceiveCallback(const ReceiveParams& params,
     receive_info.data = data;
     scoped_ptr<base::ListValue> args = serial::OnReceive::Create(receive_info);
     scoped_ptr<extensions::Event> event(
-        new extensions::Event(serial::OnReceive::kEventName, args.Pass()));
+        new extensions::Event(extensions::events::UNKNOWN,
+                              serial::OnReceive::kEventName, args.Pass()));
     PostEvent(params, event.Pass());
   }
 
@@ -110,7 +111,8 @@ void SerialEventDispatcher::ReceiveCallback(const ReceiveParams& params,
     scoped_ptr<base::ListValue> args =
         serial::OnReceiveError::Create(error_info);
     scoped_ptr<extensions::Event> event(
-        new extensions::Event(serial::OnReceiveError::kEventName, args.Pass()));
+        new extensions::Event(extensions::events::UNKNOWN,
+                              serial::OnReceiveError::kEventName, args.Pass()));
     PostEvent(params, event.Pass());
     if (ShouldPauseOnReceiveError(error)) {
       SerialConnection* connection =