Add demangle utility to Dartium's dart:html. Demangle typedef names in UserVisibleName.

tools/dom/src/native_DOMImplementation.dart

 // 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.
 
 part of html;
 
 class _ConsoleVariables {
   Map<String, Object> _data = new Map<String, Object>();
 
   /**
@@ skipping 369 matching lines @@
   /**
    * Removes the trailing dot from an expression ending in a dot.
    * This method is used as Library prefixes include a trailing dot when using
    * the C Dart debugger API.
    */
   static String stripTrailingDot(String str) =>
     (str != null && str[str.length - 1] == '.') ? str.substring(0, str.length - 1) : str;
 
   static String addTrailingDot(String str) => '${str}.';
 
+  static String demangle(String str) {
+    var atPos = str.indexOf('@');
+    return atPos == -1 ? str : str.substring(0, atPos);
+  }
+
   static bool isNoSuchMethodError(obj) => obj is NoSuchMethodError;
 
   static bool _isBuiltinType(ClassMirror cls) {
     // TODO(vsm): Find a less hackish way to do this.
     LibraryMirror lib = cls.owner;
     String libName = lib.uri.toString();
     return libName.startsWith('dart:');
   }
 
   static void register(Document document, String tag, Type type,
@@ skipping 204 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }