Disable WebrtcCastApiTEst.Basics

This test is failing only on Win7 and a DISABLED_ prefix couldn't
disable it. Make sure this test is disabled for now.

TBR=kalman@chromium.org
BUG=314971

Review URL: https://codereview.chromium.org/59383007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233024 0039d316-1c4b-4281-b951-d872f2087c98