This shouldn't result in any logical changes. I've done a quick smoke
test by building a local Android engine and running Flutter gallery, no
compile errors or other obvious issues.
Applied by running `/ci/format.sh | patch -p0` with the altered script
added in flutter/engine#16500. I did locally modify the script slightly
further so it would run against all Java files in the repo instead of
just modified ones.
This allows applications to start a Flutter engine instance during app startup
and keep it running throughout the app process' lifetime.
FlutterActivity subclasses can override createFlutterNativeView to provide a
preinitialized FlutterNativeView instance and override retainFlutterNativeView
to signal that the FlutterNativeView should be kept alive when the activity
is destroyed.
This factors the functionality that was in `FlutterActivity`
to live in `FlutterActivityDelegate`. This will allow the creation of a
`FlutterFragmentActivity` that has the same core functionality, which in
turn unlocks certain Android plugins that choose to require the v4
support library (like Google Sign-In).
https://github.com/flutter/flutter/issues/10072
FragmentActivity is required for plugins that use auto managed Google APIs, such as Google Sign-In. Requires flutter/flutter#9036 to land so that gradle builds include FragmentActivity.
