Add WorkaroundNewWindowFlash study (50% nightly)

[goodov]

Resolves #1177

[github-actions]

✅ Test Seed Generated Successfully

Seed Details

Parameter	Value
Version	pull/1178@7d5bec8a5cbf7c5386bea59bb57c6c22b53da256
Uploaded	Tue, 13 Aug 2024 12:42:53 GMT
PR commit	736206c
Base commit	a189a97
Merge commit	7d5bec8
Serial number	760681755b77b9cba884e4bb386ab724

Applying the test seed

1. Desktop: Launch the browser with --variations-pr=1178.
   Android: Set the command line to --variations-pr=1178 in debug menu, restart the browser.
   iOS: Set Variations PR to 1178 in Brave Core Switches debug menu, restart the browser.
2. Wait 5-10 seconds to fetch the seed.
3. Restart the browser to apply the seed.
4. Ensure Active Variations section at brave://version starts with the expected seed version (see below).

[kjozwiak]

Nightly verification(s)

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

Brave | 1.70.66 Chromium: 128.0.6613.27 (Official Build) nightly (64-bit)
-- | --
Revision | 667a3d64bcaa33f50347e567971f37eeb76758aa
OS | Windows 11 Version 23H2 (Build 22631.3958)

WorkaroundNewWindowFlash:Enabled Case - PASSED

• launched 1.70.66 Chromium: 128.0.6613.27 using brave.exe --enable-logging=stderr --variations-pr=1178
• relaunched once again using brave.exe --enable-logging=stderr --variations-pr=1178
• ensured that pull/1178@7d5bec8a5cbf7c5386bea59bb57c6c22b53da256 is appearing under brave://version
• ensured that WorkaroundNewWindowFlash:Enabled via brave://version
• ensured that minimizing/maximizing the browser didn't create a white flash when the window is being restored
• ensured that opening Brave doesn't produce a white flash

workingExample.mp4

WorkaroundNewWindowFlash:Default Case - PASSED

• launched 1.70.66 Chromium: 128.0.6613.27 using brave.exe --enable-logging=stderr --variations-pr=1178
• relaunched once again using brave.exe --enable-logging=stderr --variations-pr=1178
• ensured that pull/1178@7d5bec8a5cbf7c5386bea59bb57c6c22b53da256 is appearing under brave://version
• ensured that WorkaroundNewWindowFlash:Enabled via brave://version
• ensured that minimizing/maximizing the browser produced a white flash when the window is being restored
• ensured that opening Brave produced a white flash

brokenExample.mp4

[kjozwiak]

Uplift into production approved after deliberating with @brave/uplift-approvers. QA has verified the PR on Nightly as per #1178 (comment).