Flaky FlutterChannelsTest tests #126084
Description
I'm seeing rollers fail on the Linux Mac Unopt task with various failures in the FlutterChannelsTest. For example: https://ci.chromium.org/ui/p/flutter/builders/try/Linux%20mac_unopt/946/overview
The run with the most failures included the following failures, but other runs on the same bot (it does 3 retries) had only a subset of these failures:
Failing tests:
-[FlutterChannelsTest testBasicMessageChannelInvokeHandlerAfterChannelReleased]
-[FlutterChannelsTest testBasicMessageChannelTaskQueue]
-[FlutterChannelsTest testEventChannelTaskQueue]
-[FlutterChannelsTest testMethodChannelInvokeHandlerAfterChannelReleased]
-[FlutterChannelsTest testMethodChannelTaskQueue]