37971 Update dependencies (a: accessibility, cla: yes, d: examples, team, team: gallery)

37981 Give _runFlutterTest the ability to validate command output (cla: yes, team)

37983 Revert “Moved the default BinaryMessenger instance to ServicesBinding… (a: accessibility, a: tests, cla: yes, f: cupertino, f: material design, framework, team)

37984 Fix some typos in flutter/dev/bots/README.md (cla: yes, team)

37994 Remove no-constant-update-2018, the underlying issue has been resolved. (cla: yes, tool)

38101 Catch filesystem exception from flutter create (cla: yes, tool)

38102 Fix type error hidden by implicit downcasts (cla: yes, tool)