Disable TestReattachAfterCrash on Mac OSX

TestReattachAfterCrash exhibits flaky behavior on Mac OSX. Disable it on Mac OSX.

BUG=163411
R=nasko@chromium.org
TBR=kaznacheev@chromium.org

Review URL: https://codereview.chromium.org/112673006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242632 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242632