dart2js: Use an abstract Name class for names in the generated JavaScript ast.

pkg/compiler/lib/src/js_backend/frequency_namer.dart

Index: pkg/compiler/lib/src/js_backend/frequency_namer.dart
diff --git a/pkg/compiler/lib/src/js_backend/frequency_namer.dart b/pkg/compiler/lib/src/js_backend/frequency_namer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5b995b6bd03e58e4e3e88c4e77ea92b09ac43d06
--- /dev/null
+++ b/pkg/compiler/lib/src/js_backend/frequency_namer.dart
@@ -0,0 +1,15 @@
+// Copyright (c) 2015, 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 js_backend;
+
+class FrequencyNamer extends Namer {
+  FrequencyNamer(Compiler compiler) : super(compiler);
+
+  jsAst.Name getFreshName(String proposedName, Set<String> usedNames,
+      Map<String, String> suggestedNames,
+      {bool sanitizeForNatives: false, bool sanitizeForAnnotations: false}) {
+    return null;
+  }
+}