YouTube pre-roll ads appearing in certain cases

[LaurenWags]

Description

In the case below I'm able to reproduce getting a pre-roll add on a YouTube video every time with 1.30.x. It does not reproduce with 1.28.106 (current Release)

Steps to Reproduce

Steps:

1. Clean profile with Nightly 1.30.44 Chromium: 93.0.4577.51
2. Visit https://www.youtube.com/
3. Search hot ones and click on the First We Feast channel (at top of page)
4. Click on Videos within the First We Feast channel
5. Choose the video below:

Actual result:

Every time I do this on 1.30.x I get a pre-roll ad

Expected result:

No pre-roll ad like 1.28.106

Reproduces how often:

easily

Brave version (brave://version info)

Brave | 1.30.44 Chromium: 93.0.4577.51 (Official Build) nightly (x86_64)
-- | --
Revision | 762d21050e2da59930c784c09b134d0b0b148188-refs/branch-heads/4577@{#915}
OS | macOS Version 10.15.7 (Build 19H1323)

Version/Channel Information:

• Can you reproduce this issue with the current release? no
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the nightly channel? yes

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 @brave/legacy_qa @antonok-edm

[kjozwiak]

Reproduced several times on Win 10 x64 using the following build while I was investigating #17669.

Brave | 1.30.43 Chromium: 93.0.4577.51 (Official Build) nightly (64-bit)
-- | --
Revision | 762d21050e2da59930c784c09b134d0b0b148188-refs/branch-heads/4577@{#915}
OS | Windows 10 OS Version 2009 (Build 19042.1165)

Once I started playing a video, I noticed that there was a re-roll add. Pressing Skip. Only seen it a handful of times but it's definitely happening.

[antonok-edm]

Confirmed it's not caused by brave/brave-core#9673 or any of the subsequent followups - it still occurs on 1.30.22, which is before all of them.

Also, I was able to reproduce it using #brave-adblock-cosmetic-filtering-native disabled in brave://flags, so it's not specific to native cosmetic filtering.

[antonok-edm]

I tracked it down to brave/brave-core#9545.

Something is preventing cosmetic filtering scriptlets from being injected into the page - entering JSON.parse in the devtools console from a youtube page with a preroll add should show Proxy {length: 2, name: "parse"}, but instead it shows up as native code.

[LaurenWags]

Verified passed with

Brave | 1.30.59 Chromium: 93.0.4577.58 (Official Build) beta (x86_64)
-- | --
Revision | c4410ece044414ea42fa4ba328d08195e818a99c-refs/branch-heads/4577@{#1076}
OS | macOS Version 10.15.7 (Build 19H1323)

Verified STR from description 5x, confirmed no pre-roll ads observed.
Viewed various YT videos, confirmed no pre-roll ads observed.

---

Verification passed on

Brave | 1.30.59 Chromium: 93.0.4577.58 (Official Build) beta (64-bit)
-- | --
Revision | c4410ece044414ea42fa4ba328d08195e818a99c-refs/branch-heads/4577@{#1076}
OS | Windows 10 OS Version 2009 (Build 19043.1165)

Verified STR from description 4x, confirmed no pre-roll ads observed.
Viewed various YT videos, confirmed no pre-roll ads observed.

---

Verification PASSED using

Brave	1.30.63 Chromium: 93.0.4577.63 (Official Build) beta (64-bit)
Revision	ff5c0da2ec0adeaed5550e6c7e98417dac77d98a-refs/branch-heads/4577@{#1135}
OS	Linux

Verified STR from description 10x, plus additional testing around the issue/area; confirmed no pre-roll ads were observed.
Viewed various YT videos, confirmed no pre-roll ads were observed.