Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

pkg/compiler/lib/src/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.
 
 library dart2js.library_loader;
 
 import 'dart:async';
 import 'dart2jslib.dart'
     show Compiler,
          CompilerTask,
@@ skipping 1014 matching lines @@
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 
   Future processLibraryTags(LibraryElement library) {
     return task.processLibraryTags(this, library);
   }
 }