Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/RTCDTMFSender.idl

Index: Source/modules/mediastream/RTCDTMFSender.idl
diff --git a/Source/modules/mediastream/RTCDTMFSender.idl b/Source/modules/mediastream/RTCDTMFSender.idl
index ff3b6da025d4608eae006f063acbea672af5a923..c06a48cf746e1ebf7e9ed27ab5b11da7cb3978ee 100644
--- a/Source/modules/mediastream/RTCDTMFSender.idl
+++ b/Source/modules/mediastream/RTCDTMFSender.idl
@@ -25,9 +25,8 @@
 
 [
     NoInterfaceObject,
-    ActiveDOMObject,
-    EventTarget
-] interface RTCDTMFSender {
+    ActiveDOMObject
+] interface RTCDTMFSender : EventTarget {
     readonly attribute boolean canInsertDTMF;
     readonly attribute MediaStreamTrack track;
     readonly attribute DOMString toneBuffer;
@@ -37,13 +36,4 @@
     [RaisesException] void insertDTMF(DOMString tones, optional long duration, optional long interToneGap);
 
     attribute EventListener ontonechange;
-
-    // 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);
 };