13176 Add repeatCount to FlutterKeyEvent (cla: yes)

13177 Update compiler to Clang 10. (cla: yes)

13179 Update timeout_microseconds to timeout in docs (cla: yes)

13180 Use the fixtures mechanism for txt unit-tests and benchmarks. (cla: yes)

13181 Revert “Update compiler to Clang 10.” (cla: yes)

13182 If we get a ‘down’ event, add that device to the active devices. (cla: yes)

13185 Adding firefox_installer.dart (affects: tests, cla: yes, platform-web)

13187 [web] Environment variable to disable felt snapshot (cla: yes, platform-web)