Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/EventTarget.dartdoc

Index: lib/html/doc/interface/EventTarget.dartdoc
diff --git a/lib/html/doc/interface/EventTarget.dartdoc b/lib/html/doc/interface/EventTarget.dartdoc
index 2f702ab33eb616f01a6875a8772b7e4835e2e3db..c5bf5323e8a48e66e817190ba5a36096d2efa584 100644
--- a/lib/html/doc/interface/EventTarget.dartdoc
+++ b/lib/html/doc/interface/EventTarget.dartdoc
@@ -2,11 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// WARNING:
-//   This file contains documentation that is merged into the real source.
-//   Do not make code changes here.
+// WARNING: Do not edit - generated code.
 
-interface EventListenerList {
+abstract class EventListenerList {
   EventListenerList add(EventListener handler, [bool useCapture]);
 
   EventListenerList remove(EventListener handler, [bool useCapture]);
@@ -14,15 +12,15 @@ interface EventListenerList {
   bool dispatch(Event evt);
 }
 
-interface Events {
+abstract class Events {
   EventListenerList operator [](String type);
 }
 
 /// @domName EventTarget
-interface EventTarget {
+abstract class EventTarget {
 
   /** @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent */
-  final Events on;
+  abstract Events get on;
 
   /** @domName EventTarget.addEventListener */
   void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);