Move js library back into compiler directory.

sdk/lib/_internal/compiler/js_lib/isolate_patch.dart

 // Copyright (c) 2012, 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.
 
 // Patch file for the dart:isolate library.
 
 import 'dart:_js_helper' show patch;
 import 'dart:_isolate_helper' show CapabilityImpl,
                                    CloseToken,
                                    IsolateNatives,
@@ skipping 131 matching lines @@
   factory RawReceivePort([void handler(event)]) {
     return new RawReceivePortImpl(handler);
   }
 }
 
 @patch
 class Capability {
   @patch
   factory Capability() = CapabilityImpl;
 }