Add 'part of' in dart2js code.

lib/compiler/implementation/scanner/scanner_task.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 scanner;
+
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name => 'Scanner';
 
   void scanLibrary(LibraryElement library) {
     var compilationUnit = library.entryCompilationUnit;
     compiler.log("scanning library ${compilationUnit.script.name}");
     scan(compilationUnit);
   }
 
@@ skipping 17 matching lines @@
   dietParse(CompilationUnitElement compilationUnit, Token tokens) {
     measure(() {
       Function idGenerator = compiler.getNextFreeClassId;
       ElementListener listener =
           new ElementListener(compiler, compilationUnit, idGenerator);
       PartialParser parser = new PartialParser(listener);
       parser.parseUnit(tokens);
     });
   }
 }