Reduce Language not farbling HTTP headers of subresources

[pilgrim-brave]

Easily reproducible on the QA page, open devtools and network tab and refresh the page. The primary resource's Accept-Language request header is farbled, but subresources like site.css are not.

[kjozwiak]

@brave/qa-team STR/Cases can be found via brave/brave-core#14338 (comment). Used the screenshot example that @pilgrim-brave provided via #24282 (comment) as guidance and received confirmation that the pass looks good 👍

@pilgrim-brave also recommended running through https://dev-pages.brave.software/fingerprinting/headers.html as well. Basically ensuring that Sub-resource has the correct values.

[LaurenWags]

Verified with

Brave | 1.42.97 Chromium: 104.0.5112.102 (Official Build) (x86_64)
-- | --
Revision | 8e5396254975ef939f2ef7d0bd334e48a052b536-refs/branch-heads/5112@{#1478}
OS | macOS Version 12.5 (Build 21G72)

Reproduced the original issue mentioned via #24282 (comment) using the following STR/Cases:

• installed 1.42.95 Chromium: 104.0.5112.81
• restarted the browser and ensured that DisableReduceLanguage:Enabled
• double checked and ensured that Prevent sites from fingerprinting me based on my language preferences was enabled via brave://settings/shields
• added several languages via brave://settings/languages
• visited https://dev-pages.brave.software/index.html and opened the DevTools
• under the Network tab, clicked on Disable cache
• refreshed https://dev-pages.brave.software/index.html once again

Farbled	Not farbled	Not farbled

Verified steps above using 1.42.97 Chromium: 104.0.5112.102:

Languages selected	Farbled	Farbled	Farbled

Also ran through tests on https://dev-pages.brave.software/fingerprinting/headers.html as per #24282 (comment):

Languages	Block Fingerprinting (Default)	Aggressively Block Fingerprinting	Allow Fingerprinting

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.42.97 Chromium: 104.0.5112.102 (Official Build) (64-bit)
-- | --
Revision | 8e5396254975ef939f2ef7d0bd334e48a052b536-refs/branch-heads/5112@{#1478}
OS | Windows 10 Version 21H2 (Build 19044.1889)

Reproduced the original issue mentioned via #24282 (comment) using the following STR/Cases:

• installed 1.42.95 Chromium: 104.0.5112.81
• restarted the browser and ensured that DisableReduceLanguage:Enabled
• double checked and ensured that Prevent sites from fingerprinting me based on my language preferences was enabled via brave://settings/shields
• added several languages via brave://settings/languages
• visited https://dev-pages.brave.software/index.html and opened the DevTools
• under the Network tab, clicked on Disable cache
• refreshed https://dev-pages.brave.software/index.html once again

Farbled	Not farbled	Not farbled

Verified steps above using 1.42.97 Chromium: 104.0.5112.102:

Languages selected	Farbled	Farbled	Farbled

Also ran through tests on https://dev-pages.brave.software/fingerprinting/headers.html as per #24282 (comment):

Languages	Block Fingerprinting (Default)	Aggressively Block Fingerprinting	Allow Fingerprinting

[kjozwiak]

Verification PASSED on Samsung Tablet S8 Ultra running Android 12 using the following build(s):

Brave | 1.42.97 Chromium: 104.0.5112.102 (Official Build) (64-bit)
-- | --
Revision | 8e5396254975ef939f2ef7d0bd334e48a052b536-refs/branch-heads/5112@{#1478}
OS | Android 12; Build/SP1A.210812.016

Languages	Block Fingerprinting (Default)	Aggressively Block Fingerprinting	Allow Fingerprinting

[kjozwiak]

Verification PASSED on Samsung S10+ running Android 12 using the following build(s):

Brave | 1.42.97 Chromium: 104.0.5112.102 (Official Build) (64-bit)
-- | --
Revision | 8e5396254975ef939f2ef7d0bd334e48a052b536-refs/branch-heads/5112@{#1478}
OS | Android 12; Build/SP1A.210812.016

Languages	Block Fingerprinting (Default)	Aggressively Block Fingerprinting	Allow Fingerprinting