Avoid mangling the name of native methods.

frog/element.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Any abstract representation of a dart element.  This includes
  * [Library], [Type] and [Member].
  */
 class Element implements Hashable {
   // TODO(jimhug): Make name final when we can do it for Library.
   /** The user-visible name of this [Element]. */
   String name;
 
   /** A safe name to use for this [Element] in generated JS code. */
   String _jsname;
 
   /** The lexically/logically enclosing [Element] for lookups. */
   Element _enclosingElement;
 
   Element(this.name, this._enclosingElement) {
-    _jsname = world.toJsIdentifier(name);
+    if (name !== null) {
+      String mangled = mangleJsName();
+      assert(!mangled.contains(':'));
+      _jsname = mangled;
+    }
   }
 
   // TODO - walk tree
   Library get library() => null;
 
   /** A source location for messages to the user about this [Element]. */
   SourceSpan get span() => null;
 
   /** Should this element be treated as native JS? */
   bool get isNative() => false;
@@ skipping 12 matching lines @@
   /**
    * [jsname] priority of this element, if two elements conflict.
    * Higher one gets the name.
    */
   int get jsnamePriority() => isNative ? 2 : (library.isCore ? 1 : 0);
 
   /** Resolve types and other references in the [Element]. */
   void resolve() {}
 
   /**
+   * By default we mangle the JS name of an element to avoid
+   * giving them names that clash with JS keywords.
+   */
+  String mangleJsName() => world.toJsIdentifier(name);
+
+  /**
    * Any type parameters that this element defines to setup a generic
    * type resolution context.  This is currently used for both generic
    * types and the semi-magical generic factory methods - but it will
    * not be used for any other members in the current dart language.
    */
   // TODO(jimhug): Confirm whether or not these are still on factories.
   List<ParameterType> get typeParameters() => null;
 
   List<Type> get typeArgsInOrder() => const [];
 
@@ skipping 100 matching lines @@
   /** This must be the highest possible priority. */
   int get jsnamePriority() => 10;
 
   /** A source location for messages to the user about this [Element]. */
   SourceSpan get span() => declaringElement.span;
 
   /** A library for messages. */
   Library get library() => declaringElement.library;
 
 }