Nuke DOMImplementation.hasFeature test for Dart support.

client/dart.js

 // 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.
 
 // Bootstrap support for Dart scripts on the page as this script.
 
-// TODO: remove hasFeature clause once fully migrated to webkitStartDart.
 if (navigator.webkitStartDart) {
   navigator.webkitStartDart();
-} else if (!document.implementation.hasFeature('dart', '1.0')) {
+} else {
   window.addEventListener("DOMContentLoaded", function (e) {
       // Fall back to compiled JS.
       var scripts = document.getElementsByTagName("script");
       var length = scripts.length;
       for (var i = 0; i < length; ++i) {
         if (scripts[i].type == "application/dart") {
           // Remap foo.dart to foo.js.
           // TODO:
           // - Support in-browser compilation.
           // - Handle inline Dart scripts.
           if (scripts[i].src && scripts[i].src != '') {
             var script = document.createElement('script');
             script.src = scripts[i].src + '.js';
             var parent = scripts[i].parentNode;
             parent.replaceChild(script, scripts[i]);
           }
         }
       }
     }, false);
 }