Add support for not including platform.js in build output

pkg/polymer/lib/src/build/polyfill_injector.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.
 
 /// Includes any additional polyfills that may needed by the deployed app.
 library polymer.src.build.polyfill_injector;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
@@ skipping 82 matching lines @@
       }
 
       _addScriptFirst(urlSegment) {
         document.head.nodes.insert(0, parseFragment(
               '<script src="packages/$urlSegment"></script>\n'));
       }
 
       var suffix = options.releaseMode ? '.js' : '.concat.js';
       if (!dartSupportFound) _addScriptFirst('web_components/dart_support.js');
       // platform.js should come before all other scripts.
-      if (!platformJsFound) _addScriptFirst('web_components/platform$suffix');
+      if (!platformJsFound && options.injectPlatformJs) {
+        _addScriptFirst('web_components/platform$suffix');
+      }
 
       transform.addOutput(
           new Asset.fromString(transform.primaryInput.id, document.outerHtml));
     });
   }
 }
 
 final _platformJS = new RegExp(r'platform.*\.js', caseSensitive: false);
 final _dartSupportJS = new RegExp(r'dart_support.js', caseSensitive: false);