WebGoldenComparator constructor Null safety

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

WebGoldenComparator class

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