[Desktop] WebGL Drawing FP blocking not working correctly when FP set to Strict

[LaurenWags]

Description

When testing on our QA test pages for FP farbling, I noticed that if FP is set to Strict, WebGL Drawing does not appear to be working correctly.

Per discussion with @pes10k logging this and tagging @pilgrim-brave to hopefully take a look.

Steps to Reproduce

1. Clean profile 1.11.92
2. Navigate to https://dev-pages.bravesoftware.com/farbling.html and https://dev-pages.brave.software/farbling.html
3. Confirm FP setting is Standard in shields
4. Generate FPs on both pages, confirm they look as expected. (ie. - they are the same across each row on each page but differ between pages for all that have Version - 1.11)

5. Restart browser.
6. For both pages, change FP to Allow All in shields
7. Generate FPs, confirm they look as expected. (ie - they are the same across each row and the same on both pages)

8. Restart browser.
9. For both pages, change FP to Strict in shields
   10 Generate FPs.

Actual result:

WebGL Drawing is the same on both pages

Expected result:

Expected WebGL Drawing to be different on both pages (but the same across its row)

Reproduces how often:

easily

Brave version (brave://version info)

1.11.92

Version/Channel Information:

• Can you reproduce this issue with the current release? n/a, strict setting not available in 1.10.x
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the dev channel? yes (1.11.x)
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

cc @rebron @brave/legacy_qa

[btlechowski]

Reproduced on:

Brave	1.12.102 Chromium: 84.0.4147.89 (Official Build) dev (64-bit)
Revision	19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS	Ubuntu 18.04 LTS

[pes10k]

Thanks all for documenting this!

cc @pilgrim-brave

[pes10k]

I've updated the test page text so that is clear that the farbling-style protections (different per-session, per-etld+1) should only hold in "standard" protections, and not "strict" (bc in strict we just block WebGL drawing all together, since its too difficult to randomize), and so blocking will look identical in all origins.

Thanks @LaurenWags for reporting!

[pes10k]

i've labeled "not actionable" only bc there isn't a "it was pete's test fault, not Mark's code fault" option ;)

[LaurenWags]

Removing QA/Yes tag since it's been tagged closed/not-actionable, but I did confirm both pages now reflect that WebGL Drawing farbling is only available in "standard" mode 👍