Set up the infrastructure for Extension event metrics.

extensions/browser/api/hid/hid_device_manager.cc

Index: extensions/browser/api/hid/hid_device_manager.cc
diff --git a/extensions/browser/api/hid/hid_device_manager.cc b/extensions/browser/api/hid/hid_device_manager.cc
index 5a6403c87c95b01bc5fb318e76adb27b5c647ee1..10afa1d702d0fbbba81b5008ba218eb7cf6c26e4 100644
--- a/extensions/browser/api/hid/hid_device_manager.cc
+++ b/extensions/browser/api/hid/hid_device_manager.cc
@@ -287,7 +287,8 @@ void HidDeviceManager::OnEnumerationComplete(
 void HidDeviceManager::DispatchEvent(const std::string& event_name,
                                      scoped_ptr<base::ListValue> event_args,
                                      scoped_refptr<HidDeviceInfo> device_info) {
-  scoped_ptr<Event> event(new Event(event_name, event_args.Pass()));
+  scoped_ptr<Event> event(
+      new Event(events::UNKNOWN, event_name, event_args.Pass()));
   event->will_dispatch_callback =
       base::Bind(&WillDispatchDeviceEvent, device_info);
   event_router_->BroadcastEvent(event.Pass());