Chore/feature attribute exists #2499

Job	Run time
test / test-dart-vm (3.3.0)	4m 17s
test / test-dart-vm (stable)	3m 51s
native_test / test-dart-native (macos-latest)	3m 8s
dart2js_test / test-dart-2js (3.3.0, chrome)	6m 33s
native_test / test-dart-native (windows-latest)	4m 52s
dart2js_test / test-dart-2js (3.3.0, firefox)	6m 37s
dart2js_test / test-dart-2js (stable, chrome)	6m 44s
ddc_test / test-dart-ddc (3.3.0, chrome)	5m 46s
dart2js_test / test-dart-2js (stable, firefox)	6m 36s
ddc_test / test-dart-ddc (3.3.0, firefox)	5m 58s
ddc_test / test-dart-ddc (stable, chrome)	5m 38s
ddc_test / test-dart-ddc (stable, firefox)	5m 48s
	1h 5m 48s

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