Add 'part of' in dart2js code.

lib/compiler/implementation/library_loader.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.
 
+part of dart2js;
+
 /**
  * [CompilerTask] for loading libraries and setting up the import/export scopes.
  */
 abstract class LibraryLoader extends CompilerTask {
   LibraryLoader(Compiler compiler) : super(compiler);
 
   /**
    * Loads the library located at [uri] and returns its [LibraryElement].
    *
    * If the library is not already loaded, the method creates the
@@ skipping 658 matching lines @@
   }
 
   /**
    * Registers all top-level entities of [library] as starting point for the
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 }