GitLab

If we find a null frame, we reject with a "Document not active"
exception.

Bug: 916656
Change-Id: If76de22eb1fd977571bb7517e6d745e3ad9077e9
Reviewed-on: https://chromium-review.googlesource.com/c/1391773
Commit-Queue: Doug Turner <dougt@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619867}