Move dart2jslib parts into separate libraries.

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

 // Copyright (c) 2014, 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.
 
 library dart2js.js_backend.patch_resolver;
 
 import '../dart2jslib.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../elements/modelx.dart';
+import '../messages.dart' show MessageKind;
 import '../tree/tree.dart';
 
 class PatchResolverTask extends CompilerTask {
   PatchResolverTask(Compiler compiler) : super(compiler);
 
   String get name => 'JavaScript patch resolver';
 
   FunctionElement resolveExternalFunction(FunctionElementX element) {
     if (element.isPatched) {
       FunctionElementX patch = element.patch;
@@ skipping 124 matching lines @@
              'patchParameterCount': patchSignature.optionalParameterCount});
       });
     } else {
       checkMatchingPatchParameters(origin,
                                    originSignature.optionalParameters,
                                    patchSignature.optionalParameters);
     }
   }
 
 }