Add 'part of' in dart2js code.

lib/compiler/implementation/js/printer.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 js;
+
 class Printer implements NodeVisitor {
   final bool shouldCompressOutput;
   leg.Compiler compiler;
   leg.CodeBuffer outBuffer;
   int indentLevel = 0;
   bool inForInit = false;
   bool atStatementBegin = false;
   final DanglingElseVisitor danglingElseVisitor;
   final Namer namer;
 
   Printer(leg.Compiler compiler)
       : shouldCompressOutput = compiler.enableMinification,
         this.compiler = compiler,
         outBuffer = new leg.CodeBuffer(),
         danglingElseVisitor = new DanglingElseVisitor(compiler),
         namer = determineRenamer(compiler.enableMinification);
-  
+
   static Namer determineRenamer(bool shouldCompressOutput) {
     // TODO(erikcorry): Re-enable the MinifyRenamer after M1.
     return new IdentityNamer();
   }
 
   void spaceOut() {
     if (!shouldCompressOutput) out(" ");
   }
   void lineOut() {
     if (!shouldCompressOutput) out("\n");
@@ skipping 943 matching lines @@
       }
       codes.add(charCodes.$0 + digit);
       newName = new String.fromCharCodes(codes);
     }
     assert(const RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
     nameNumber++;
     maps.last()[oldName] = newName;
     return newName;
   }
 }