Add 'part of' in dart2js code.

lib/compiler/implementation/scanner/string_scanner.dart

Index: lib/compiler/implementation/scanner/string_scanner.dart
diff --git a/lib/compiler/implementation/scanner/string_scanner.dart b/lib/compiler/implementation/scanner/string_scanner.dart
index 8aaf04d01ec3544d8b06b62def90af09f47fcd0f..36bcebcd69efb84f2f9078cf66ab8d11bd0801c9 100644
--- a/lib/compiler/implementation/scanner/string_scanner.dart
+++ b/lib/compiler/implementation/scanner/string_scanner.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;
+
 /**
  * Scanner that reads from a String and creates tokens that points to
  * substrings.