Use JsNames.getValid instead of implementing another (broken) version of it.

lib/compiler/implementation/namer.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.
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer {
   final Compiler compiler;
 
@@ skipping 46 matching lines @@
     List<SourceString> names = selector.getOrderedNamedArguments();
     for (SourceString argumentName in names) {
       buffer.add(@'$');
       argumentName.printOn(buffer);
     }
     return '${privateName(lib, name)}\$${selector.argumentCount}$buffer';
   }
 
   String instanceFieldName(LibraryElement lib, SourceString name) {
     String proposedName = privateName(lib, name);
-    if (jsReserved.contains(proposedName)) {
-      return '$proposedName\$';
-    }
-    return proposedName;
+    return JsNames.getValid(proposedName);
   }
 
   String setterName(LibraryElement lib, SourceString name) {
     return 'set\$${privateName(lib, name)}';
   }
 
   String getterName(LibraryElement lib, SourceString name) {
     return 'get\$${privateName(lib, name)}';
   }
 
@@ skipping 128 matching lines @@
   }
 
   String safeName(String name) {
     if (jsReserved.contains(name) || name.startsWith('\$')) {
       name = "\$$name";
       assert(!jsReserved.contains(name));
     }
     return name;
   }
 }