I'm hitting this too. Since yesterday.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a12f08001af67413c4571e6e9e974196789783dc

commit a12f08001af67413c4571e6e9e974196789783dc
Author: Owen Min <zmin@chromium.org>
Date: Thu Oct 12 14:58:43 2017

Support recommanded content setting policies

Some content settings preferences should only created by policies which could be at recommanded level.

Bug:  773791 
Change-Id: I478db5d9f16ded0cdc049f05756954b4a9641e96
Reviewed-on: https://chromium-review.googlesource.com/713744
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508349}
[modify] https://crrev.com/a12f08001af67413c4571e6e9e974196789783dc/components/content_settings/core/browser/content_settings_policy_provider.cc

Patch landed. vakh@ and rogerm@, could you please verify the fix? Thanks a lot.

Should policy_templates.json be updated to reflect that content setting policies can now be recommended?

|can_be_recommended| in policy_temmplates.json affects the documentation and ADM/ADMX file. https://cs.chromium.org/chromium/src/components/policy/resources/policy_templates.json?q=can_be_recommended&sq=package:chromium&dr=C&l=124
Because there is no way for user to override the value of this preference, I don't think it worth to show this policy in the ADMX file of recommended policies.

In the other word, admin should still set this policy in mandatory level in most of case . The CL above just make sure if any admin set this policy via Registry manually, Chrome is Ok with that.

Hm, the statement in line 126 ("all policies can be at the recommended level") is false, as evidenced by this bug :) "This only affects the template generation" is also false, because it affects the publicly-facing documentation at https://www.chromium.org/administrators/policy-list-3#PluginsAllowedForUrls as well.

Yes, I agree this documentation is out of date and confuses people. What it trying to say is:

"This only affects the template generation"
1) This tag only affects templets, documentation and something similar. It doesn't affect the behavior of Chrome at all.
"all policies can be at the recommended level. The default is False." 
2) All policies are allowed to use this tag. The value of this tag is false by default. However, policies still accepts recommended level value (by default) even the tag is false. It's the situation of most of polices today.

In the other word, |can_be_recommended| is designed for the policies that user is able to override. For others, there is no difference between mandatory and recommended.

I can reword the description of this doc. But I don't think it's necessary to 	
expressly tell admin that PluginsAllowedForURLs can be used in the recommended level.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dc08a2ffb0ba3cb2c342346544f734dcdce67cdf

commit dc08a2ffb0ba3cb2c342346544f734dcdce67cdf
Author: Owen Min <zmin@chromium.org>
Date: Fri Oct 27 14:49:28 2017

Improving documentation of policy_templates.json

Improving the doc of |can_be_mandatory| and |can_be_recommended|.

Bug:  773791 
Change-Id: I3fc8d52d91184d393878eca23ae09c7d5de97a79
Reviewed-on: https://chromium-review.googlesource.com/738172
Commit-Queue: Owen Min <zmin@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512181}
[modify] https://crrev.com/dc08a2ffb0ba3cb2c342346544f734dcdce67cdf/components/policy/resources/policy_templates.json