Split js_backend into multiple libraries

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

 // 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;
+part of js_backend.namer;
 
 abstract class _NamerName extends jsAst.Name {
   int get _kind;
   _NamerName get _target => this;
 
   String toString() {
     if (DEBUG_MODE) {
       return 'Name($key)';
     }
     throw new UnsupportedError("Cannot convert a name to a string");
@@ skipping 195 matching lines @@
 
   @override
   int compareTo(_NamerName other) => _target.compareTo(other);
 
   @override
   bool operator ==(other) => _target == other;
 
   @override
   int get hashCode => _target.hashCode;
 }