Revert "ScaffoldMessenger" - #65257

2020-09-03T17:08:21.642332: stdout: I/flutter (28358): > Animated images@Media
2020-09-03T17:08:24.942930: stdout: I/flutter (28358): < Success
2020-09-03T17:08:24.943962: stdout: I/flutter (28358): > Video@Media
2020-09-03T17:08:25.375250: stdout: I/flutter (28358): > VideoDemo initController "butterfly" 
2020-09-03T17:08:25.386199: stdout: I/flutter (28358): > VideoDemo initController "bee" 
2020-09-03T17:08:25.421674: stdout: I/flutter (28358): (The following exception is now available via WidgetTester.takeException:)
2020-09-03T17:08:25.427394: stdout: I/flutter (28358): ══╡  ╞══════════════════════════════════════════════════════════════════════════════════════════════
2020-09-03T17:08:25.428547: stdout: I/flutter (28358): ════════════════════════════════════════════════════════════════════════════════════════════════════
stdout: I/flutter (28358): (If WidgetTester.takeException is called, the above exception will be ignored. If it is not, then the above exception will be dumped when another exception is caught by the framework or when the test ends, whichever happens first, and then the test will fail due to having not caught or expected the exception.)
stdout: I/flutter (28358): ══╡  ╞══════════════════════════════════════════════════════════════════════════════════════════════
stdout: I/flutter (28358): ════════════════════════════════════════════════════════════════════════════════════════════════════
stdout: I/flutter (28358): 01:57 +0 ~1: flutter gallery transitions on e2e all demos [E]
stdout: I/flutter (28358):   Test failed. See exception logs above.
stdout: I/flutter (28358):   The test description was: all demos
stdout: I/flutter (28358):   
2020-09-03T17:08:25.432474: stdout: I/flutter (28358): 01:57 +0 ~1 -1: (tearDownAll)
2020-09-03T17:08:25.449954: stdout: I/flutter (28358): 01:57 +1 ~1 -1: Some tests failed.
2020-09-03T17:08:25.523096: stdout: Failure Details:
2020-09-03T17:08:25.523357: stdout: Failure in method: all demos
2020-09-03T17:08:25.523692: stdout: 
2020-09-03T17:08:25.524226: stdout: end of failure 1
2020-09-03T17:08:25.524394: stdout: 
2020-09-03T17:08:25.524716: stdout: 
2020-09-03T17:08:25.525: stdout: 
2020-09-03T17:08:25.559286: stdout: Stopping application instance.
2020-09-03T17:08:25.707562: stdout: I/flutter (28358): 01:57 +1 ~1 -1: flutter gallery transitions on e2e all demos
2020-09-03T17:08:25.708118: stdout: I/flutter (28358): Another exception was thrown: Instance of 'ErrorSummary'
2020-09-03T17:08:26.140122: stdout: I/flutter (28358): > VideoDemo dispose
2020-09-03T17:08:26.143215: stdout: I/flutter (28358): < VideoDemo dispose
2020-09-03T17:08:26.192091: stdout: I/flutter (28358): > VideoDemo initController "butterfly" 
2020-09-03T17:08:26.198203: stdout: I/flutter (28358): > VideoDemo initController "bee" 
2020-09-03T17:08:26.238713: stdout: I/flutter (28358): ══╡  ╞══════════════════════════════════════════════════════════════════════════════════════════════
2020-09-03T17:08:26.238962: stdout: I/flutter (28358): ════════════════════════════════════════════════════════════════════════════════════════════════════
2020-09-03T17:08:26.758921: stderr: Driver tests failed: 1