Test scripts: Replace a guard that was optimistically removed, fixing a break on Windows.
Test scripts: Replace a guard that was optimistically removed, fixing a break on Windows.

BUG=
TEST=tools/test.py

Review URL: https://chromiumcodereview.appspot.com//10697018

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@9205 260f80e4-7a28-3924-810f-c04153c831b5

dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk