The goal here is to have a great standalone `android_engine_test` suite
that [replaces
`scenario_app/android`](https://github.com/flutter/flutter/pull/160992).
No test is _functionally_ changed in this PR, but overview of changes:
- Finished renaming the suite `android_engine_tests` instead of
`flutter_driver_android`
- Added instructions and an environment variable for local generation of
golden-files (`UPDATE_GOLDENS=1`)
- Added explanations of the individual tests, where they live, and how
to run them locally
- Added a hybrid-composition (HC, not TLHC, which is already tested)
test
- Renamed "other_smiley" to "surface_texture_smiley" (and renamed the
original to "surface_producer_smiley")
- Removed unnecessary ".android" suffix (we will not run this on
anything but Android)
- Added a `tool/deflake.dart` to run a test suite 10x (or custom) times
locally to try and determine flakiness
After this PR, I'll add flags to let you control variants and name the
screenshots accordingly, i.e.:
- API v34 or v35
- OpenGLES or Vulkan (will require an `AndroidManifest.xml` edit during
the test instrumentation)
