Pass in DART_SDK from batch file on Windows.

utils/pub/sdk/pub.bat

Index: utils/pub/sdk/pub.bat
diff --git a/utils/pub/sdk/pub.bat b/utils/pub/sdk/pub.bat
index bc47b4953f1b1d6d9e5e65cb450da32307afcdce..8d974f416ebd15541a7d4b213460c4de139e7f08 100644
--- a/utils/pub/sdk/pub.bat
+++ b/utils/pub/sdk/pub.bat
@@ -1,18 +1,17 @@
 @echo off
-REM Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-REM for details. All rights reserved. Use of this source code is governed by a
-REM BSD-style license that can be found in the LICENSE file.
+:: 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.
 
-REM Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
-REM structure.
+:: Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
+:: structure.
 
 set SCRIPTPATH=%~dp0
 
-REM Does the string have a trailing slash? If so, remove it.
+:: Does the string have a trailing slash? If so, remove it.
 if %SCRIPTPATH:~-1%==\ set SCRIPTPATH=%SCRIPTPATH:~0,-1%
 
-REM Canonicalize the direction of the slashes.
-set script=%*
-set script=%script:\=/%
+:: Set DART_SDK so pub can find SDK packages.
+set DART_SDK=%SCRIPTPATH%\..\
 
-"%SCRIPTPATH%\dart.exe" "%SCRIPTPATH%\..\util\pub\pub.dart" %script%
+"%SCRIPTPATH%\dart.exe" "%SCRIPTPATH%\..\util\pub\pub.dart" %*