feat(android): Automatically call FullyDrawnReporter to improve production PGOs

[mrousavy]

Summary:

Since Android 12 the Google PlayStore automatically profiles cold starts of new apps on user devices to optimize them for subsequent launches (affects JVM, not native).

This works most effectively if the app reliably calls reportFullyDrawn() once its content has been... fully drawn.

See App startup time: Android Vitals for more information

This is super hard to test isolated, but it should improve performance in production by making these PlayStore profiles more accurate, allowing Android to optimize production apps better as it understands when TTFD (Time-To-Full-Display) actually happens, which is hard to tell for Android in a non-native Android app (i.e. react-native, with asynchronous rendering and whatnot).

Since react-native renders the main UI asynchronously, I do expect this change to make a performance difference in production, but this is merely an assumption and not a tested claim.

Btw., this does not call reportFullyDrawn() directly, but instead uses androidx' FullyDrawnReporter, which is collaborative - meaning this works well in brownfield apps and apps can also extend this to register their reporter to delay their TTFD reporting.

By default, it is enabled and reports on CONTENT_APPEARED.

I added a feature flag which allows users (brownfield?) to disable it by overriding isFullyDrawnReportingEnabled() to return false.

Changelog:

[ANDROID] [ADDED] - Automatically call FullyDrawnReporter to improve production performance via profiles

Test Plan:

Isolated

Make sure reportFullyDrawn() is called:

adb logcat -s ActivityTaskManager

Before this PR you'll see something like

Displayed com.app/.MainActivity: +400ms

After this PR you'll see something like

Fully drawn com.app/.MainActivity: +1.4s

too.

Production

Ideally PlayStore can optimize the bytecode better with more accurate TTFDs, and startup time should decrease, but that is speculation.

[mrousavy]

Claude says you can inspect the generated profiles;

adb shell killall -s SIGUSR1 com.your.app   # force ART to save the profile
adb shell pm dump-profiles com.your.app     # writes readable dump to /data/misc/profman/
adb pull /data/misc/profman/com.your.app-primary.prof.txt

Haven't tried myself though.