Add USBConnectionEvent to webusb module.

Source/modules/webusb/USBConnectionEventInit.idl

Index: Source/modules/webusb/USBConnectionEventInit.idl
diff --git a/Source/modules/background_sync/SyncEventInit.idl b/Source/modules/webusb/USBConnectionEventInit.idl
similarity index 59%
copy from Source/modules/background_sync/SyncEventInit.idl
copy to Source/modules/webusb/USBConnectionEventInit.idl
index a7d2f51233d2312d5707e7b68707a4b4183cb234..05115ad81e2e19980fd25a68da8ce02684f6e17d 100644
--- a/Source/modules/background_sync/SyncEventInit.idl
+++ b/Source/modules/webusb/USBConnectionEventInit.idl
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-dictionary SyncEventInit : ExtendableEventInit {
-    required SyncRegistration registration;
+// http://reillyeon.github.io/webusb/#events
+
+dictionary USBConnectionEventInit : EventInit {
+    USBDevice device;
 };