Brave News should require explicit opt-in

[petemill]

Previously it was deemed ok to not require an explicit opt-in for Brave News' remote network fetch because:

1. It waited for user interaction with the feature before making any network requests. In other words, it did not request data for the feature if the user did not actively use it, whether it was already on for that user's region or not.
2. The network requests use Brave's Private CDN, meaning no identity or behaviorally-identifiable information is transmitted. Every user requests the same feed, and the specific article images are all padded to be the same size.

However, in the interests of caution we want to require the users to explicitly opt-in to the feature, including the privacy policy, before making any network requests.

[stephendonner]

Verified PASSED using

Brave	1.26.43 Chromium: 91.0.4472.77 (Official Build) beta (x86_64)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	macOS Version 11.4 (Build 20F71)

Migration - have previously used Brave Today in 1.25.68

Steps:

1. new profile, launch 1.25.68
2. open a new-tab page
3. click on Customize
4. click on Brave Today
5. ensure Show Brave Today is defaulted to On
6. scroll down and view a few sheets worth of Brave Today articles
7. quit Brave
8. save profile off
9. install 1.26.43
10. rename original profile to Brave-Browser-Beta
11. launch 1.26.43
12. open a new-tab page
13. scroll down
14. confirm you get shown a panel with Show Brave News and No thanks
15. click on No thanks
16. confirm the panel is dismissed, and Brave News doesn't display
17. click on Customize
18. click on Brave News
19. click the toggle for Show Brave News to On
20. click the X to dismiss the dialog
21. scroll down
22. confirm you see the panel again
23. this time, click on Show Brave News
24. confirm Brave News' content now displays

example	example	example	example	example	example

Migration - have NOT previously used Brave Today in 1.25.68

Steps:

1. new profile, launch 1.25.68
2. open a new-tab page
3. click on Customize
4. click on Brave Today
5. ensure Show Brave Today is defaulted to On
6. do NOT scroll down
7. quit Brave
8. save profile off
9. install 1.26.43
10. rename original profile to Brave-Browser-Beta
11. launch 1.26.43
12. open a new-tab page
13. scroll down
14. confirm you get shown a panel with Show Brave News and No thanks
15. click on No thanks
16. confirm the panel is dismissed, and Brave News doesn't display
17. click on Customize
18. click on Brave News
19. click the toggle for Show Brave News to On
20. click the X to dismiss the dialog
21. scroll down
22. confirm you see the panel again
23. this time, click on Show Brave News
24. confirm Brave News' content now displays

example	example	example	example	example	example

New profile - 1.26.43

1. new profile, launch 1.26.43
2. open a new-tab page
3. click on Customize
4. click on Brave Today
5. ensure Show Brave Today is defaulted to On
6. scroll down
7. confirm you get shown a panel with Show Brave News and No thanks
8. click on No thanks
9. confirm the panel is dismissed, and Brave News doesn't display
10. click on Customize
11. click on Brave News
12. click the toggle for Show Brave News to On
13. click the X to dismiss the dialog
14. scroll down
15. confirm you see the panel again
16. this time, click on Show Brave News
17. confirm Brave News' content now displays

example	example	example	example	example

Filed #15977 for the Brave News source list showing 0 in the Customize Dashboard's Brave News panel, when not-yet opted in.

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Verification passed on

<!--StartFragment-->
Brave | 1.26.47 Chromium: 91.0.4472.77&nbsp;(Official Build)&nbsp;beta&nbsp;(64-bit)
-- | --
Revision | 1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS | Windows&nbsp;10 OS Version 2004 (Build 19041.985)

<!--EndFragment-->

New profile - `1.26.47`

example	example	example	example	example

- Encountered https://github.com//issues/15977

Upgrade profile - Not used Brave News in `1.25.x`

1.25.x	1.26.x	1.26.x	1.26.x	1.26.x	1.26.x

Upgrade profile - used Brave News in `1.25.x`

1.25.x	1.25.x	1.26.x	1.26.x	1.26.x

---

Verification passed on

Brave	1.26.45 Chromium: 91.0.4472.77 (Official Build) beta (64-bit)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	Ubuntu 18.04 LTS

Clean profile

Upgrade profile - Not used Brave News in `1.25.x`

Upgrade profile - used Brave News in `1.25.x`