Dial back on host-checked testing.
Dial back on host-checked testing.

Seems to be causing timeouts on Safari builders, and there's no added
value from running these tests in host-checked mode on multiple
platforms.

Review URL: https://codereview.chromium.org//13975007

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@21359 260f80e4-7a28-3924-810f-c04153c831b5

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