Disable HistoryWebUIRealBackendTest for being non-PDT-friendly

TBR=dubroy

Review URL: https://codereview.chromium.org/57303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232680 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232680