Enable viewport_test.dart's shuffling (#87319)
Enable viewport_test.dart's shuffling (#87319)

This PR fixed the problem that has prevented viewport_test.dart being shuffled.


tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter