[Perf] Fix JSON processing on UI thread

[atuchin-m]

Found here: #35693 (comment)

[atuchin-m]

The urls we parse:
https://brave-today-cdn.brave.com/sources.global.json
https://brave-today-cdn.brave.com/brave-today/feed.en_USjson

One of the code parts:
https://github.com/brave/brave-core/blob/master/components/brave_news/browser/publishers_controller.cc#L199C8-L285

The same pattern is used across the brave_news code.

[petemill]

Just to note that we're agreed the main performance improvement here should first be to remove the processing off the main thread, and not adjust the request timing. We can improve that but need to consider the needs of Desktop, Android and the various UI which needs the data.

[atuchin-m]

a linked issue: #35778

[kjozwiak]

@atuchin-m mind double checking/ensuring that the performance issues have been resolved once we get 1.63.x builds with the above fix? Some context via https://bravesoftware.slack.com/archives/CHGKGMHDJ/p1707869423133049.

[kjozwiak]

Going to add the QA/Yes as we can basically run through some spot checks and ensure that Brave News is working correctly/not crashing as per brave/brave-core#21833 (comment). The above requires 1.63.154 or higher for 1.63.x verification 👍

[kjozwiak]

Verification PASSED on Pixel 6 running Android 14 using the following build(s):

Brave | 1.63.155 Chromium: 122.0.6261.29 (Official Build) (64-bit)
--- | ---
Revision | b2be2c6f5b7340629f672ce706f5bfd62b113f82
OS | Android 14; Build/AP11.231215.009; 34; REL

• ensured that the Brave News onboarding card is being displayed by default via NTP without any issues
  • ensured that the modal/card is animated/working as expected in terms of performance (not seeing any jank)
• ensured that enabling & disabling the feature within Settings works as expected
  • ensured when Brave News is disabled, it doesn't appear within NTP
  • ensured once Brave News is enabled once again, it's visible/scrollable via NTP (ensured there's no visible performance issues)
• ensured that scrolling through the Brave News feed is a smooth experience
• ensured that inline ads are being displayed within the news feed
  • ensured that tapping/clicking on inline ads works as expected (opens the tab/no crashes etc..)
• ensured that tapping on cards opens the website/content without any issues
• ensured that Load new content works as expected when adding feeds from Popular, Suggestions & Channels
• ensured that tapping/clicking on Learn more about your data opens the website within the WebUI without issues
  • ensured that pressing X closes the website and returns the user back into the Settings page where they can enable news

[stephendonner]

Verification PASSED using

Brave | 1.63.155 Chromium: 122.0.6261.29 (Official Build) (x86_64)
-- | --
Revision | b2be2c6f5b7340629f672ce706f5bfd62b113f82
OS | macOS Version 14.4 (Build 23E5196e)

Steps:

1. installed 1.63.155
2. launched Brave
3. cilcked the Learn More link on the Enable Brave News popup
4. navigated back
5. confirmed the page did NOT crash
6. clicked on Turn on Brave News
7. confirmed the publishers loaded
8. confirmed the (main) feed loaded
9. disabled Brave News
10. enabled Brave News
11. confirmed the publishers loaded
12. confirmed the (main) feed loaded
13. disabled Brave news
14. refreshed the page
15. enabled Brave News
16. confirmed the publishers loaded

Confirmed the (main) feed loaded and was dynamically rebuilt/reloaded, after toggling On/Off, without any crashing or hanging

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