Add the allowlist support to DelayAsyncScriptExecution

Design doc:
https://docs.google.com/document/d/1xOYUw6bX93Y-Avo9nbdtpuEYoTFHj4tAHit6TcLfEJQ/edit#

This CL introduces a new option kCrossSiteWithAllowList in the
kDelayAsyncScriptExecution feature, that only applies delays if given
script urls are matched with the allowlist.

The original motivation of this change is fixing the current limitation
of LazyEmbeds. At the moment there is no way to delay the iframe load
timing if the frame is hidden or very small, and unfortunately some
popular embed provider loads iframes with that approach along with
dynamically inserted iframes via the bootstrap JavaScript. We're going
to solve this issue by delaying the script execution that dynamically
inserts iframes, with the allowlist approach.

This CL decides "what" to delay to address the issue, but it doesn't
change "how" to delay. We still don't have a reasonable hypothesis, so
we rely on the existing DelayAsyncScriptExecution logic (milestone +
time based limit).

To make the experiment analysis easier, we add the option
(kCrossSiteWithAllowListReportOnly) that only reports the metrics if the
url is matched, without applying any delays.

This CL won't change the default behavior.

Change-Id: I01f4431d9b0ad5c7772f3bfd15288feab868309f
Bug: 1354512, 1340837
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3868637
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Commit-Queue: Shunya Shishido <sisidovski@chromium.org>
Reviewed-by: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1047287}