Disable flaky test PrerenderBrowserTest.PrerenderCancelMainFrameRedirectUnsupportedScheme

BUG=347164
TBR=cbentzel@chromium.org

Review URL: https://codereview.chromium.org/181743002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253519 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253519