Add 'part of' in dart2js code.

lib/compiler/implementation/scanner/scanner_task.dart

Index: lib/compiler/implementation/scanner/scanner_task.dart
diff --git a/lib/compiler/implementation/scanner/scanner_task.dart b/lib/compiler/implementation/scanner/scanner_task.dart
index 171a145ee1fe3ff8af8ca9d7e65e2c036273bb1d..63b9381639aa57e2a55d6312e65a3e3afa14fbf5 100644
--- a/lib/compiler/implementation/scanner/scanner_task.dart
+++ b/lib/compiler/implementation/scanner/scanner_task.dart
@@ -2,6 +2,8 @@
 // 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 scanner;
+
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name => 'Scanner';