DefaultWebGoldenComparator constructor Null safety

1. Flutter
2. flutter_test
3. DefaultWebGoldenComparator
4. DefaultWebGoldenComparator constructor

DefaultWebGoldenComparator class

1. Constructors
2. DefaultWebGoldenComparator
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. compare
8. getTestUri
9. noSuchMethod
10. toString
11. update
12. Operators
13. operator ==