Splitting interop support so `dart_support.js` is no longer required.

pkg/polymer/lib/src/build/linter.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.
 
 /// Logic to validate that developers are correctly using Polymer constructs.
 /// This is mainly used to produce warnings for feedback in the editor.
 library polymer.src.build.linter;
 
 import 'dart:async';
 import 'dart:convert';
@@ skipping 291 matching lines @@
     var src = node.attributes['src'];
 
     if (isDart) {
       if (_dartTagSeen) _logger.warning(ONLY_ONE_TAG, span: node.sourceSpan);
       if (_isEntryPoint && _polymerExperimentalHtmlSeen) {
         _logger.warning(NO_DART_SCRIPT_AND_EXPERIMENTAL, span: node.sourceSpan);
       }
       _dartTagSeen = true;
     }
 
+    if (src != null && src.endsWith('web_components/dart_support.js')) {
+      _logger.warning(DART_SUPPORT_NO_LONGER_REQUIRED, span: node.sourceSpan);
+    }
+
     var isEmpty = node.innerHtml.trim() == '';
 
     if (src == null) {
       if (isDart && isEmpty) {
         _logger.warning(SCRIPT_TAG_SEEMS_EMPTY, span: node.sourceSpan);
       }
       return;
     }
 
     if (src.endsWith('.dart') && !isDart) {
@@ skipping 126 matching lines @@
     upDirCount = segments.length - 2;
   }
   var reachOutPrefix = '../' * upDirCount;
   return USE_POLYMER_HTML.create({'reachOutPrefix': reachOutPrefix});
 }
 
 const List<String> INTERNALLY_DEFINED_ELEMENTS = 
     const ['auto-binding-dart', 'polymer-element'];
 const List<String> AUTO_BINDING_ELEMENTS =
     const ['auto-binding-dart', 'auto-binding'];