Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/RTCDataChannel.idl

Index: Source/modules/mediastream/RTCDataChannel.idl
diff --git a/Source/modules/mediastream/RTCDataChannel.idl b/Source/modules/mediastream/RTCDataChannel.idl
index b4263df90d84531d3e0bbc8c7e57fef1e878a4fe..5abf290e91b38123fd2b99a820ea0eebc65a6e87 100644
--- a/Source/modules/mediastream/RTCDataChannel.idl
+++ b/Source/modules/mediastream/RTCDataChannel.idl
@@ -23,9 +23,8 @@
  */
 
 [
-    NoInterfaceObject,
-    EventTarget
-] interface RTCDataChannel {
+    NoInterfaceObject
+] interface RTCDataChannel : EventTarget {
     readonly attribute DOMString label;
     readonly attribute boolean reliable;
     readonly attribute DOMString readyState;
@@ -44,13 +43,4 @@
     attribute EventListener onerror;
     attribute EventListener onclose;
     attribute EventListener onmessage;
-
-    // EventTarget interface
-    void addEventListener(DOMString type,
-                          EventListener listener,
-                          optional boolean useCapture);
-    void removeEventListener(DOMString type,
-                             EventListener listener,
-                             optional boolean useCapture);
-    [RaisesException] boolean dispatchEvent(Event event);
 };