Sleep before moving directory on Windows.

Gives 7zip more time to finish extracting before we access the
directory.

BUG=

Review URL: https://codereview.chromium.org//11151030

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@13670 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed