* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Roll the engine.

This engine includes a VM that defaults to sync-async.

flutter/engine@c8eeee4 Roll the Dart VM.

Enable --sync-async in Flutter.
Fixes #16801 

This reverts commit 39d7f22a.

This reverts commit b0b2c007.

* 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.

* Ignore extraneous error messages outside of one skipped test

* Fix analysis error

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.)