37416 Add MediaQuery.systemGestureInsets to support Android Q (cla: yes, customer: crowd, framework, severe: new feature, ▣ platform-android)

37508 build bundle with assemble (cla: yes, tool)

37526 catch errors during gradle update (cla: yes, tool)

37544 Replace ButtonBar.bar method with ButtonBarTheme (cla: yes, d: examples, f: material design, framework, severe: API break, team, team: gallery)

37642 Unit test for build.dart::GenSnapshot (cla: yes, tool)

37645 Update CONTRIBUTING.md (cla: yes, team)

37646 Instrument pending timers in tests (a: tests, cla: yes, framework)