Mark http/tests/pointer-lock/iframe-sandboxed-allow-pointer-lock.html as crashing

Crashes reliably for me in Debug (hits an ASSERT), might be flaky in release.

BUG=306280
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/26925003

git-svn-id: svn://svn.chromium.org/blink/trunk@159388 bbb929c8-8fbe-4397-9dbb-9b2b20218538