Fix build on Arm64 Windows

[mherrmann]

Resolves brave/brave-browser#35975.

One difference of this new implementation is that the persisted flag is now not stored in / as

"updateclientdata": {
    "<Widevine component ID>": {
        "brave_upstream_has_arm64_widevine": "true"
    }
}

but instead as

"brave_upstream_has_arm64_widevine": "true"

The previous value in updateclientdata does not need to be cleaned up because it was never set for any user. (Upstream has not yet made Arm64 Widevine available, so the condition never triggered.)

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• 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 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/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Please test that Widevine still works on Arm64 Windows. For more concrete instructions, please see for instance the Test Plan at the bottom of #18695.

[emerick]

LGTM. Is this something that's unit-testable? Might be good if we could have something that verifies writing/reading that pref, even if a follow-up.

[MadhaviSeelam]

Verification PASSED using

Brave | 1.64.74 Chromium: 122.0.6261.43 (Official Build) beta (arm64)
-- | --
Revision | b03db955df4f1c679cb7c2ae8ebfd331d5c29276
OS | Windows 11 Version 23H2 (Build 22631.3085)

Netflix - PASSED

Steps:

1. installed 1.64.74
2. launched Brave
3. loaded netflix.com
4. clicked on the Sign In link
5. entered my credentials
6. clicked on the Sign In button
7. confirmed I got prompted to Install and run Widevine
8. clicked Allow
9. clicked on Brave QA avatar
10. clicked to play Tiny creatures Arizona

Confirmed the content was streamed in High-Definition (HD) quality (through visual inspection)

Widevine prompt	HD content

Amazon Prime - PASSED

Steps:

1. installed 1.64.74
2. launched Brave
3. loaded amazon.com
4. clicked on Prime Video
5. logged in
6. confirmed I was prompted to Install and run Widevine
7. clicked on Allow
8. clicked to play Cars Life 3: The Royal Heist

Confirmed the content was streamed in High-Definition (HD) quality, "Best" quality level @ 1080p (6.48 GB per hour)

Widevine prompt	HD content

HBOMax - PASSED

Steps:

1. installed 1.64.74
2. launched Brave
3. loaded hbomax.com
4. clicked on the Sign In button
5. clicked Sign in to your account
6. clicked Sign in With a Provider button
7. clicked on QA/avatar
8. confirmed I was prompted to Install and run Widevine
9. clicked to play Tom & Jerry

Confirmed the content was streamed in High-Definition (HD) quality, through visual inspection

Widevine prompt	HD content

Bitmovin.com - PASSED

Steps:

1. Installed 1.64.74
2. launched Brave
3. visit https://bitmovin.com/demos/drm in a new tab page
4. confirmed I got prompted to Install and run Google Widevine
5. clicked Allow
6. played the video for protected DRM stream
7. Confirmed the content was streamed in High-Definition (HD) quality (through visual inspection)

Widevine prompt	HD content

Widevine component details:

Confirmed via brave://components that Widevine Content Decryption Module - Version: 4.10.2710.0 was downloaded, in all cases

brave://components	WidevineCdm folder