* Turn support for sync-async on in Flutter. With this feature
execution of async functions starts immediately instead of it
being delayed by one microtask tick.
* Address review comments.
* Adjust some stack trace expectations which are slightly different with
--sync-async turned on.
Also:
* Provide a better message when you lerp from infinity to finity
constraints.
* Make the striped marker support RTL.
* By popular demand, dump a warning to the console the first time
a particular Flex overflows. (Resets on hot reload.)
