Tweak toString() for better type inference

tools/dom/scripts/systemhtml.py

 #!/usr/bin/python
 # 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.
 
 """This module provides shared functionality for the system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 import logging
@@ skipping 39 matching lines @@
     'ConsoleBase.timeEnd',
     'ConsoleBase.timeStamp',
     'ConsoleBase.trace',
     'ConsoleBase.warn',
     'WebKitCSSKeyframesRule.insertRule',
     'CSSStyleDeclaration.setProperty',
     'CSSStyleDeclaration.__propertyQuery__',
     'Document.createNodeIterator',
     'Document.createTreeWalker',
     'DOMException.name',
+    'DOMException.toString',
     'Element.createShadowRoot',
     'Element.insertAdjacentElement',
     'Element.insertAdjacentHTML',
     'Element.insertAdjacentText',
     'Element.remove',
     'Element.shadowRoot',
     'Element.matches',
     'ElementEvents.mouseWheel',
     'ElementEvents.transitionEnd',
     'FileReader.result',
+    'HTMLAnchorElement.toString',
+    'HTMLAreaElement.toString',
     'HTMLTableElement.createTBody',
     'IDBCursor.next',
     'IDBDatabase.transaction',
     'IDBDatabase.transactionList',
     'IDBDatabase.transactionStore',
     'IDBDatabase.transactionStores',
     'KeyboardEvent.initKeyboardEvent',
     'Location.origin',
+    'Location.toString',
     'MouseEvent.offsetX',
     'MouseEvent.offsetY',
     'Navigator.language',
     'Navigator.webkitGetUserMedia',
     'ScriptProcessorNode._setEventListener',
     'URL.createObjectURL',
     'URL.createObjectUrlFromSource',
     'URL.createObjectUrlFromStream',
     'URL.createObjectUrlFromBlob',
     'URL.revokeObjectURL',
+    'URL.toString',
     'WheelEvent.deltaMode',
     'WheelEvent.wheelDeltaX',
     'WheelEvent.wheelDeltaY',
     'Window.cancelAnimationFrame',
     'Window.console',
     'Window.document',
     'Window.indexedDB',
     'Window.location',
     'Window.open',
     'Window.requestAnimationFrame',
@@ skipping 1171 matching lines @@
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def AddTypeEntry(self, library_name, idl_name, dart_name):
     self._libraries[library_name].AddTypeEntry(idl_name, dart_name)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)