ScopedTaskEnvironmentTest LifetimeObserver sets a life time observer but never cleans it.
This means that any use of ScopedTaskEnvironment after that will case a crash on 

https://cs.chromium.org/chromium/src/base/test/scoped_task_environment.cc?sq=package:chromium&g=0&l=156

This is causing crashes when running base_unittests on Chrome ios.

caused by https://chromium-review.googlesource.com/c/chromium/src/+/1251449