Disable ProcessOnce on Ash due to flakiness.

BUG=317592
TBR=mpearson

Review URL: https://codereview.chromium.org/59273003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234290 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234290