Fix leak in UbertokenFetcher unittests.

Follow-up to https://codereview.chromium.org/136723009.

Review URL: https://codereview.chromium.org/143123003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245937 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245937