Only include chromevox_test_data in isolated swarming tests for chromeos builds.

BUG=338749
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/141523011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248069 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248069