navigator.userAgent farbling not applied in workers

[pilgrim-brave]

[GeetaSarvadnya]

@pilgrim-brave Can you please link the test plan?

[pilgrim-brave]

Test plan:

1. Visit https://dev-pages.brave.software/farbling.html
2. In Brave Shields panel, change Fingerprinting to "Allow all"
3. Click 'Generate fingerprints'
4. In 'User Agent' row, all columns should show the same hash value. Note this hash value for later step.
5. In Brave Shields panel, change Fingerprinting to "Blocked (strict)"
6. Refresh page
7. Click 'Generate fingerprints'
8. In 'User Agent' row, all columns should show the same hash value. This hash value should be different than the hash value in step 4.

[GeetaSarvadnya]

Verification passed on

Brave | 1.18.69 Chromium: 87.0.4280.88 (Official Build) (64-bit)
-- | --
Revision | 89e2380a3e36c3464b5dd1302349b1382549290d-refs/branch-heads/4280@{#1761}
OS | Windows 10 OS Version 2004 (Build 19041.630)

• Verified the test plan from navigator.userAgent farbling not applied in workers #12230 (comment)
• Verified that User-Agent row, all columns have the same hash value when Fingerprinting value is allowed in the shield
  
• Verified that User-Agent row, all columns have the same hash value but different than the above step when Fingerprinting value is blocked and strict in the shield
  

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Verification passed on

Brave	1.18.70 Chromium: 87.0.4280.101 (Official Build) (64-bit)
Revision	9407c80213cda69c2b7abcb4fa8e3f74488f4956-refs/branch-heads/4280@{#1807}
OS	Ubuntu 18.04 LTS

• Verified the test plan from navigator.userAgent farbling not applied in workers #12230 (comment)
• Verified that User-Agent row, all columns have the same hash value when Fingerprinting value is allowed in the shield
  
• Verified that User-Agent row, all columns have the same hash value but different than the above step when Fingerprinting value is blocked and strict in the shield