VR: Do not fire window.rAF while presenting

As per the associated bug, we're reverting an extra call to
window.requestAnimaionFrame. Separate code already triggers a rAF when
presentation starts.

BUG=718246

Change-Id: I5bf961749d80476572f1610a3992e62a4e6a5301
Reviewed-on: https://chromium-review.googlesource.com/628963
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497034}
1 file changed