Send kUAModel and kUAPlatformVersion CHs when requested.

[mkarolin]

Resolves brave/brave-browser#29875

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[pes10k]

This looks terrific! Did not realize such a (seemingly) small change would need so much code. Thank you for sorting this out!

Just to verify, the initial build value for the clamped version will be “0”, but we could change it to something else (like “x”) using griffin?

[mkarolin]

Thanks @pes10k, a lot of the changes are for tests. Yes, the default value is set to "0", but the parameter type is a string, so it can take "x" (I used "x" in one of the tests).

[mkarolin]

Rebased and squashed.

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.53.4 Chromium: 113.0.5672.53 (Official Build) nightly (64-bit)
-- | --
Revision | 12f5dac35d12e8f4e72d7dd11df557ef93bc046f-refs/branch-heads/5672@{#703}
OS | Windows 11 Version 22H2 (Build 22621.1555)

Using the STR/Cases outlined via brave/brave-browser#29875 (comment), reproduced the using 1.52.77 Chromium: 113.0.5672.53. However, I could only reproduce the issue with this link . Seems like this link loaded fine.

1.52.77 Chromium: 113.0.5672.53	1.52.77 Chromium: 113.0.5672.53

Using the STR/Cases mentioned above, verified that both websites are correctly loading as per the following:

Example	Example	Example