Some extension tests for Android are written as chrome mochitests:
https://searchfox.org/mozilla-central/rev/325c1a707819602feff736f129cb36055ba6d94f/mobile/android/components/extensions/test/mochitest/chrome.ini

They should be rewritten as plain mochitests (and be added to mochitest.ini, because there is no plan to run chrome mochitests on GeckoView. Some of these tests can't currently run on GeckoView, because of unimplemented APIs (e.g. those that rely on browserAction and pageAction).

bug 1610641 removed many tests; when the features are restored, new tests will be added.

There is only one left: https://searchfox.org/mozilla-central/rev/0c97a6410ff018c22e65a0cbe4e5f2ca4581b22e/mobile/android/components/extensions/test/mochitest/chrome.ini#7

... but the options_ui logic has changed significantly. It's probably not relevant any more. Agi will check whether the new tests cover the tests, and if so, remove this chrome.ini file and the last remaining test: https://searchfox.org/mozilla-central/rev/0c97a6410ff018c22e65a0cbe4e5f2ca4581b22e/mobile/android/components/extensions/test/mochitest/test_ext_options_ui.html