Making ScriptProcessorNode not an EventTarget.

tools/dom/templates/html/impl/impl_ScriptProcessorNode.darttemplate

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+part of $LIBRARY;
+
+$(ANNOTATIONS)class $CLASSNAME$EXTENDS$NATIVESPEC {
+  Stream<AudioProcessingEvent> _eventStream;
+
+  /**
+   * Get a Stream that fires events when AudioProcessingEvents occur.
+   * This particular stream is special in that it only allows one listener to a
+   * given stream. Converting the returned Stream [asBroadcast] will likely ruin
+   * the soft-real-time properties which which these events are fired and can
+   * be processed.
+   */
+  Stream<AudioProcessingEvent> get onAudioProcess {
+    if (_eventStream == null) {
+      var controller = new StreamController();
+      var callback = (audioData) { 
+          if (controller.hasSubscribers) {
+            // This stream is a strange combination of broadcast and single
+            // subscriber streams. We only allow one listener, but if there is
+            // no listener, we don't queue up events, we just drop them on the
+            // floor.
+            controller.add(audioData);
+          }
+        };
+$if DART2JS
+      JS('void', '#.onaudioprocess = #', this,
+          convertDartClosureToJS(callback, 1));
+$else
+      // TODO(podivilov): Implement on Dartium.
+$endif
+
+      _eventStream = controller.stream;
+    }
+    return _eventStream;
+  }
+$!MEMBERS
+}