Put a nasty sleep() on Windows.
Put a nasty sleep() on Windows.

We get "file in use" errors between downloading and extracting archives, so sleep for a bit.

BUG=

Review URL: https://codereview.chromium.org//11146022

git-svn-id: a962b240025cf0577aa172e20f49ccb159ba6be1@13668 260f80e4-7a28-3924-810f-c04153c831b5

maxwellpeterson-wf/pub,dart-lang/pub,computmaxer/pub,dart-lang/pub,cjkao/dart-pub