Adding 'part of html' to all files which are used by dart:html.

sdk/lib/html/templates/html/impl/impl_AudioContext.darttemplate

 // Copyright (c) 2012, 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 html;
+
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME() => _$(CLASSNAME)FactoryProvider.create$CLASSNAME();
 $!MEMBERS
 $if DART2JS
   GainNode createGain() {
     if (JS('bool', '#.createGain !== undefined', this)) {
       return JS('GainNode', '#.createGain()', this);
     } else {
       return JS('GainNode', '#.createGainNode()', this);
     }
   }
 
   ScriptProcessorNode createScriptProcessor(int bufferSize,
       [int numberOfInputChannels, int numberOfOutputChannels]) {
     var function = JS('dynamic', '#.createScriptProcessor || '
         '#.createJavaScriptNode', this, this);
     if (?numberOfOutputChannels) {
       return JS('ScriptProcessorNode', '#.call(#, #, #, #)', function, this,
           bufferSize, numberOfInputChannels, numberOfOutputChannels);
     } else if (?numberOfInputChannels) {
       return JS('ScriptProcessorNode', '#.call(#, #, #)', function, this,
           bufferSize, numberOfInputChannels);
     } else {
       return JS('ScriptProcessorNode', '#.call(#, #)', function, this,
           bufferSize);
     }
   }
 $endif
 }