SamplingClock constructor Null safety

1. Flutter
2. gestures
3. SamplingClock
4. SamplingClock constructor

SamplingClock class

1. Constructors
2. SamplingClock
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. now
9. stopwatch
10. toString
11. Operators
12. operator ==