Better mangling in frog for fixing parts of issue 1837.

frog/leg/ssa/js_names.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.
 
 class JsNames {
   static final javaScriptKeywords = const <String>[
     // These are current keywords
     "break", "delete", "function", "return", "typeof", "case", "do", "if",
     "switch", "var", "catch", "else", "in", "this", "void", "continue",
     "false", "instanceof", "throw", "while", "debugger", "finally", "new",
@@ skipping 155 matching lines @@
   }
 
   // TODO(ngeoffray): only the namer should call this method.
   // Eventually move it there.
   /*
    * Returns a name that does not clash with reserved JS keywords,
    * and also ensures it won't clash with other identifiers.
    */
   static String getValid(String name) {
     if (reserved.contains(name)) {
-      name = '\$$name';
-      assert(!reserved.contains(name));
+      return getValid('\$$name');
     } else if (name.contains(@'$')) {
       name = name.replaceAll(@'$', @'$$');
     }
     return name;
   }
 }