Add support for source maps in deferred libraries.

tests/compiler/dart2js/source_map_deferred_validator_test_file.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 pop_pop_win.game_web;
 
-import 'platform_web.dart';
-import 'package:pop_pop_win/pop_pop_win.dart';
+import 'source_map_deferred_validator_test_lib.dart' deferred as def;
 
 void main() {
-  startGame(new PlatformWeb());
-}
+  def.loadLibrary().then((_) {
+    () {
+      var helloClass = new def.HelloClass();
+      helloClass.printHello();
+    }();
+  });
+}