Revert "Dartium JS Interop enabled."

sdk/lib/js/dart2js/js_dart2js.dart

 // 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.
 
 /**
  * Support for interoperating with JavaScript.
  *
  * This library provides access to JavaScript objects from Dart, allowing
  * Dart code to get and set properties, and call methods of JavaScript objects
  * and invoke JavaScript functions. The library takes care of converting
@@ skipping 431 matching lines @@
   int get length {
     // Check the length honours the List contract.
     var len = JS('', '#.length', _jsObject);
     // JavaScript arrays have lengths which are unsigned 32-bit integers.
     if (JS('bool', 'typeof # === "number" && (# >>> 0) === #', len, len, len)) {
       return JS('int', '#', len);
     }
     throw new StateError('Bad JsArray length');
   }
 
-  set length(int length) { super['length'] = length; }
+  void set length(int length) { super['length'] = length; }
 
 
   // Methods overriden for better performance
 
   void add(E value) {
     callMethod('push', [value]);
   }
 
   void addAll(Iterable<E> iterable) {
     var list = (JS('bool', '# instanceof Array', iterable))
@@ skipping 164 matching lines @@
   // Dart in that context. The JS object will have a cached proxy
   // but it won't be a valid Dart object in this context.
   // For now we throw away the cached proxy, but we should be able
   // to cache proxies from multiple JS contexts and Dart isolates.
   if (dartProxy == null || !_isLocalObject(o)) {
     dartProxy = createProxy(o);
     _defineProperty(o, propertyName, dartProxy);
   }
   return dartProxy;
 }