fix linter on svg

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;
 
@@ skipping 377 matching lines @@
     }
   }
 
   /**
    * Produces warnings for misuses of on-foo event handlers, and for instanting
    * custom tags incorrectly.
    */
   void _validateNormalElement(Element node) {
     // Event handlers only allowed inside polymer-elements
     node.attributes.forEach((name, value) {
-      if (name.startsWith('on')) {
+      if (name is String && name.startsWith('on')) {
         _validateEventHandler(node, name, value);
       }
     });
 
     // Validate uses of custom-tags
     var nodeTag = node.tagName;
     var hasIsAttribute;
     var customTagName;
     if (_isCustomTag(nodeTag)) {
       // <fancy-button>
@@ skipping 120 matching lines @@
     'Make sure the script tag is placed after all HTML imports.';
 
 const String BOOT_JS_DEPRECATED =
     '"boot.js" is now deprecated. Instead, you can initialize your polymer '
     'application by calling "initPolymer()" in your main. If you don\'t have a '
     'main, then you can include our generic main by adding the following '
     'script tag to your page: \'<script type="application/dart">export '
     '"package:polymer/init.dart";</script>\'. Additionally you need to '
     'include: \'<script src="packages/browser/dart.js"></script>\' in the page '
     'too. Make sure these script tags come after all HTML imports.';