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Specifically, blocking only happens while in CCT and only if a
parameter is supplied along with the intent. The ability to do this
will be restricted to certain apps.

BUG=1149582
TEST=CustomTabActivityTest and NotificationPermissionContextTest

Change-Id: Ieb6d76ff2326406872764973ff31d81d8e088449
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2538359
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828341}