Revert "Parts must start with 'part of'" and "Attempt to fix VM build"

dart/lib/compiler/implementation/tree_validator.dart

Index: dart/lib/compiler/implementation/tree_validator.dart
diff --git a/dart/lib/compiler/implementation/tree_validator.dart b/dart/lib/compiler/implementation/tree_validator.dart
index b1dc9c191cb59736b0bca2345a70144d287b784e..bef2891dceef1d5c6c85593cc8cf74e3c0854b07 100644
--- a/dart/lib/compiler/implementation/tree_validator.dart
+++ b/dart/lib/compiler/implementation/tree_validator.dart
@@ -2,8 +2,6 @@
 // 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 dart2js;
-
 class TreeValidatorTask extends CompilerTask {
   TreeValidatorTask(Compiler compiler) : super(compiler);