Filter out _openstat query string tracker out of URLs

[fmarier]

_openstat appears to be campaign-related but when we take an example from the wild:

https://moscow.petrovich.ru/catalog/7198/138090/?_openstat=ZGlyZWN0LnlhbmRleC5ydTs0MDY1MTc3Mzs2OTk3NDY3MzE2O3lhbmRleC5ydTpwcmVtaXVt&yclid=7597867600238632462&utm_source=yandex&utm_medium=cpc&utm_campaign=MSK%7CDSA%7C40651773&utm_content=cid%7C40651773%7Cgid%7C3683802495%7Caid%7C6997467316%7Ckid%7C966577%7Cpos%7Cpremium1%7Cadtarget%7C%D0%A1%D1%83%D1%85%D0%B8%D0%B5%20%D1%81%D1%82%D1%80%D0%BE%D0%B8%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D1%8B%D0%B5%20%D1%81%D0%BC%D0%B5%D1%81%D0%B8%20%D0%B8%20%D0%B3%D0%B8%D0%B4%D1%80%D0%BE%D0%B8%D0%B7%D0%BE%D0%BB%D1%8F%D1%86%D0%B8%D1%8F%7C%D0%93%D0%B8%D0%B4%D1%80%D0%BE%D0%B8%D0%B7%D0%BE%D0%BB%D1%8F%D1%86%D0%B8%D1%8F%7Cadtarget_id%7C966577%7Csrc%7Csearch_none%7Cdvc%7Cdesktop%7Cgoalid%7C1712089&utm_term=966577%7C%7Creg%7C%D0%9C%D0%BE%D1%81%D0%BA%D0%B2%D0%B0

and decode the _openstat base64 parameter, we get:

direct.yandex.ru;40651773;6997467316;yandex.ru:premium

This refers to Yandex Direct which has to do with conversion tracking.

It's not clear that all uses of OpenStat are user-identifying though since it depends on what the payload contains.

[fmarier]

Also, it's not clear whether this service is still in operation: https://translate.google.com/translate?sl=auto&tl=en&u=https%3A%2F%2Fwww.openstat.ru%2F

[fmarier]

According to Yandex documentation the _openstat parameter is also used by https://liveinternet.ru:

You can track ad campaign results in Yandex.Direct by using independent third-party statistics systems like Openstat or LiveInternet. Just add the special parameter (the _openstat tag) to your ad link.
and that company's analytics platform is still alive.

[fmarier]

Given that this parameter does include high-entropy values in the wild and that it appears to still be in use by one company, we will add it to the filter.

[btlechowski]

Verification passed on

Brave	1.17.28 Chromium: 86.0.4240.75 (Official Build) nightly (64-bit)
Revision	c69c33933bfc72a159aceb4aeca939eb0087416c-refs/branch-heads/4240@{#1149}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#6742

Verified to Normal Window, Private Window and Private Window with Tor

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Verification PASSED on macOS 10.15.7 x64 using the following build:

Brave | 1.17.42 Chromium: 86.0.4240.99 (Official Build) nightly (x86_64)
-- | --
Revision | 002668237e13d38aabd6d11c2d216dd22b736ff2-refs/branch-heads/4240@{#1229}
OS | macOS Version 10.15.7 (Build 19H2)

• Verified the STR/Cases outlined via Add _openstat to the query filter brave-core#6742 and ensured that _openstat is being filtered out from the URL
  • ensured the above worked as expected using Tor Windows, Guest Windows, Private Browsing Windows
• Verified that https://brave5t5rjjg3s6k.onion/?_openstat=foo was also being filtered

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Verification passed on

Brave | 1.17.52 Chromium: 86.0.4240.111 (Official Build) dev (64-bit)
-- | --
Revision | b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS | Windows 10 OS Version 1903 (Build 18362.1139)

• Verified the test plan from Add _openstat to the query filter brave-core#6742
  

• Verified to Normal Window, Private Window and Private Window with Tor

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.17.68 x64 build

• Verified test plan from Add _openstat to the query filter brave-core#6742
• Verified on both normal, private tab and custom tabs

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Verification passed on Samsung Tab A with Android 10 running 1.17.68 x64 build

• Verified test plan from Add _openstat to the query filter brave-core#6742
• Verified on both normal and private tab