maintain at most single overlay for each view in hybrid composition

[2ZeroSix]

Fixed rendering of single widget in multiple overlays on top of each hybrid composition PlatformView

I wasn't able to come up with any meaningful test for this scenario (besides snapshot test on android device), would appreciate any help here.

reproduction examples:

simple case in multiple_overlays branch (from original issue): https://github.com/2ZeroSix/flutter_android_surface_activity_destroy_bug_example/tree/multiple_overlays

screenshots

	1 view	2 views
before
after

complex case in multiple_scrollable_overlays branch: https://github.com/2ZeroSix/flutter_android_surface_activity_destroy_bug_example/tree/multiple_scrollable_overlays

videos

before

FILE.2021-03-31.13.00.57.mp4

after

FILE.2021-03-31.13.01.14.mp4

List which issues are fixed by this PR. You must list at least one issue.
fixes flutter/flutter#79371

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[blasten]

I was expecting the overlay layers to be associated with two different view_ids since there are two platform views, and the fab button intersects both.

Do you mind verifying why a single view_id contain the two overlay surfaces?

[blasten]

For testing, we use the scenario app. https://github.com/flutter/engine/blob/master/testing/scenario_app/README.md#running-for-android.

The tests are in https://github.com/flutter/engine/blob/master/testing/scenario_app/android/app/src/androidTest/java/dev/flutter/scenariosui/PlatformViewUiTests.java.

Thanks for the contribution, and let me know if you encounter any issue.

[2ZeroSix]

@blasten I updated bug reproduction example https://github.com/2ZeroSix/flutter_android_surface_activity_destroy_bug_example/tree/multiple_scrollable_overlays

I found strange behavior (like a race condition) when view should jump between overlay and background layers

To fix this I just added empty fullscreen platform view.
And now I don't understand what's going on at all 🙃

video

background android view is disabled: flutter views in listview might get clipped in region of transition between background and overlay layers
background android view is enabled: everything works as expected in this pr

master:

FILE.2021-04-01.14.25.36.mp4

this pr:

FILE.2021-04-01.14.33.31.mp4

[chinmaygarde]

Do we understand the issue and/or are we making progress?

[blasten]

@chinmaygarde Hard to say without debugging it. I will take a look shortly.

[chinmaygarde]

@blasten Is this still on your plate? Is there someone else we can find to review this patch?

[blasten]

@2ZeroSix I took a closer look, and this seems reasonable. Can you add some unit tests for each of the code branches?

[chinmaygarde]

Any updates on the unit-tests?

[blasten]

Thanks for the contribution. I will take this bug, and add the tests.