Internal bugs: http://b/190767277, http://b/185423816

Using https://developer.android.com/reference/android/view/ViewTreeObserver.OnPreDrawListener to delay when Flutter's activity first draws can help solve

• getting more accurate https://developer.android.com/topic/performance/vitals/launch-time measurements
• not require a custom Flutter splash screen transition on top of the Android OS's splash screen and the subsequent Android S splash screen breaking change (b/185423816)

Things this might involve:

• Update https://flutter.dev/docs/development/ui/advanced/splash-screen#android-launch-screen
• Support a compatibility mode with the old way. Likely by letting this be configurable via FlutterView constructor argument and letting there be intent builder flags defaulting to yes on FlutterActivity/FlutterFragment/FlutterFragmentActivity