Disable AutoSizeSW test on mac because it's flaky.

BUG=299507

TBR=lazyboy@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/149783002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247741 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247741