Reduce Language fingerprinting preference causes website to break

[ShivanKaul]

Description

Navigating to https://www.ticketweb.ca/ with Reduce Language fingerprinting preference on results in an empty page. With the pref turned off, page loads fine.

Steps to Reproduce

1. Go to https://www.ticketweb.ca/ with Reduce Language fingerprinting preference in brave://settings/shields turned on

Actual result:

Expected result:

Reproduces how often:

It seems like the issue is a lack of a weight being sent in the Accept-Language header when Reduce Language pref is turned on. There's a 1/6 chance that it will be set to nothing: https://github.com/brave/brave-core/blob/master/browser/brave_shields/reduce_language_navigation_throttle.cc#L98
My Accept-Language header is en-US with Reduce Language on and en-US,en;q=0.9 with it off.

[stephendonner]

Verified PASSED using

Brave	1.41.65 Chromium: 103.0.5060.42 (Official Build) nightly (x86_64)
Revision	de0d840bf9439c31bd86bf74f065c31fdf9b208d-refs/branch-heads/5060@{#667}
OS	macOS Version 11.6.7 (Build 20G630)

---

Reproduced using:

Brave	1.41.39 Chromium: 102.0.5005.78 (Official Build) nightly (x86_64)
Revision	df6dbb5a9fd82af3f567198af2eb5fb4876ef99c-refs/branch-heads/5005_59@{#3}
OS	macOS Version 11.6.7 (Build 20G630)

Steps:

1. installed Brave
2. launched Brave
3. loaded https://ticketweb.ca
4. confirmed page rendered
5. opened brave://settings/shields
6. confirmed Prevent sites from fingerprinting me based on my language preferences was toggled to ON by default

1.41.39	brave://settings/shields

1.41.65	brave://settings/shields

[MadhaviSeelam]

Verification PASSED using

Brave | 1.41.72 Chromium: 103.0.5060.42 (Official Build) beta (64-bit)
-- | --
Revision | de0d840bf9439c31bd86bf74f065c31fdf9b208d-refs/branch-heads/5060@{#667}
OS | Windows 11 Version 21H2 (Build 22000.739)

Couldn't reproduce in older builds Beta and Nightly (1.40.100 Chromium: 102.0.5005.125 beta, 1.41.39 Chromium: 102.0.5005.78)

Page rendered as expected in 1.41.72

Steps:

• installed Brave
• launched Brave
• loaded https://ticketweb.ca
• confirmed page rendered
• opened brave://settings/shields
• confirmed Prevent sites from fingerprinting me based on my language preferences was toggled to ON by default

1.41.72	brave://settings/shields

[stephendonner]

Verified PASSED using

Brave	1.41.84 Chromium: 103.0.5060.66 (Official Build) beta (64-bit)
Revision	20b1569438a85e631d15e83eb355e3e326e5da6f-refs/branch-heads/5060@{#1066}
OS	Linux

NOTE: until things are a bit more smoothed out, this isn't enabled by default any longer, in the client, and is instead now controlled by a Griffin study.

Confirmed:

• pref is now OFF by default (see above)
• ticketweb.ca displays fine even with Prevent sites from fingerprinting me based on my language preferences toggled to ON

1.41.84	brave://settings/shields

Also, could NOT reproduce the issue in 1.41.39:

1.41.39	brave://settings/shields

[srirambv]

Removing Android label as this need to be implemented via #23918 which is blocked on #23919