Fix the pkg/http multipart test to avoid a race condition.

BUG=8843

Review URL: https://codereview.chromium.org//12374027

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/http@19263 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: 3214e883b6f075249ac65b665466c7f25e767f54
  1. lib/
  2. test/
  3. pubspec.yaml