[ios] Do not snapshot for rapid blocking of javascript popups

Rapid blocking of javascript popups can cause a crash as simultaneous
snapshots are triggered. Do not take snapshots when consecutive infobars
are popup blocking infobars.

Bug: 1018285
Change-Id: I46bca7fd8cc1f4d3f43ff28800b37c41a247f7e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999084
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Auto-Submit: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731597}