Add default autoplay whitelist to chrome://settings/content/autoplay

[btlechowski]

Steps to Reproduce

1, Clean profile
2. Go to chrome://settings/content/autoplay

Important: Default whitelist was introduced in #1089

Actual result:

pages whitelisted for autoplay are not shown in chrome://settings/content/autoplay

Expected result:

pages whitelisted for autoplay are shown in chrome://settings/content/autoplay

Reproduces how often:

always

Brave version (chrome://version info)

Brave	0.55.13 Chromium: 70.0.3538.54 (Official Build) beta (64-bit)
Revision	4f8e578b6680574714e9ed3bb9f02922b4dde40d-refs/branch-heads/3538@{#937}
OS	Windows 7

cc @pilgrim-brave @bbondy @kjozwiak @srirambv @GeetaSarvadnya @LaurenWags

[bbondy]

This is by design, users can add a Block entry for anything that is on the whitelist.

Otherwise we'd get into a bunch of UX issues like when a user re-adds then but we need to update our whitelist list, we'd need to re-add the ones a user removed. Different complications like that, but we planned for it to work like it is now.