Linux_android_emu_34 flutter_driver_android_test is flaky

[zanderso]

A SkiaGold test of a gradient is giving a black screen as in https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8733990227946223697/+/u/run_test.dart_for_flutter_driver_android_shard_and_subshard_None/stdout

The bot will probably file an issue about this tomorrow morning, but this is so flaky that I want to file this now to note that the flakiness seems to have started with the engine roll in 72e8161

[matanlurey]

@jonahwilliams is looking into this at the moment.

[matanlurey]

From chat (h/t @jason-simmons):

The log is mentioning an untriaged image for the platform_view_blue_orange_gradient_portrait.android test.

Previously I saw an issue with that test where Android sometimes does not render the expected content (see #155787)

The screenshot is now showing up as blank instead of showing landscape content while in portrait mode
(see https://flutter-gold.skia.org/detail?grouping=name%3Dt.platform_view_blue_orange_gradient_portrait.android%26source_type%3Dflutter&digest=5ba6df7acef516f7dab78587cf30ce20).

I don't know if this is another manifestation of the same underlying issue or if something else changed (possibly related to the UI/platform thread merge, which was in the engine roll linked in the issue)

[jason-simmons]

I was able to reproduce this with a local engine:

• patch dev/integration_tests/native_driver_test/test_driver/platform_view_blue_orange_gradient_main_test.dart and uncomment the autoUpdateGoldenFiles = true line
• patch dev/tools/native_driver/lib/src/goldens.dart - in _getTestFilePath override testScriptDir with a path that is not a temporary directory
• cd dev/integration_tests/native_driver_test
• run flutter --local-engine android_debug_unopt_x64 --local-engine-host host_debug_unopt drive lib/platform_view_blue_orange_gradient_main.dart

When I run this, the first screenshot captured by the test is sometimes blank. I've been able to reproduce it on a Pixel 6a and an Android API 33 emulator.

But so far I have not seen it happen if I revert the UI/platform thread merge (flutter/engine@2eedaf1)

[jonahwilliams]

If the timing for the first frame rasterization changed, then its likely that not waiting on the first frame causes some flakiness. I'm going to try using the driver method of waiting here to see if that stabilizes things: #156907

[jason-simmons]

I'm still seeing the issue after applying the flutterDriver.waitUntilFirstFrameRasterized() patch.

If I insert a delay immediately before the test's first call to nativeDriver.screenshot(), then I can see a black screen on the emulator when this happens.

[matanlurey]

Ack @jonahwilliams, should we revert and try something else?