Fix ios disk cache test exclusions.

In landing r254474, we didn't migrate an iOS test exclusion, so we
broke a few bots. Let's fix that.

R=kalman@chromium.org, kalman
BUG=None

Review URL: https://codereview.chromium.org/185683004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254554 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254554