Remove opt outs for dart:ui

[vsmenon]

Remove Dart language version opt-out for dart:ui files.

This is already ignored on a build for dart:ui, so it shouldn't change any behavior. The opt-out appears to be confusing pub analysis though. @sigurdm @mit-mit

[flutter-dashboard]

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[zanderso]

It looks like this change is causing window_hooks_integration_test.dart to fail to compile to kernel. The failing command is:

/b/s/w/ir/cache/builder/src/out/host_debug_unopt/dart-sdk/bin/dart \
/b/s/w/ir/cache/builder/src/out/host_debug_unopt/gen/frontend_server.dart.snapshot \
--enable-experiment=non-nullable \
--no-sound-null-safety \
--sdk-root /b/s/w/ir/cache/builder/src/out/host_debug_unopt/flutter_patched_sdk \
--incremental \
--target=flutter \
--packages /b/s/w/ir/cache/builder/src/flutter/testing/dart/.packages \
--output-dill /b/s/w/ir/cache/builder/src/out/window_hooks_integration_test.dart.kernel.dill \
/b/s/w/ir/cache/builder/src/flutter/testing/dart/window_hooks_integration_test.dart

Unfortunately, the logs don't have stderr from the command so it will need to be debugged locally.

[vsmenon]

Thanks, @zanderso - it looks like my out/paragraph_test.dart.kernel.dill is out of date. Do you know what step rebuilds that?

[zanderso]

In an engine checkout, flutter/testing/run_tests.py will compile all the Dart language tests and run them. This step is failing for window_hooks_integration_test.dart https://github.com/flutter/engine/blob/master/testing/run_tests.py#L177

[vsmenon]

PTAL

I had to bump window_hooks_integration_test.dart up to 2.12 as well since that pulls in dart:ui files as parts for testing. I also had to add explicit // @dart = 2.12 annotations - the pattern of reaching into ../../lib/ui from the test file seems to confuse the Dart CFE as far as language versioning. I think @ferhatb had to do similar with the web_ui files.