* Add a --strong option to the front end server so we can use strong mode with preview-dart-2.
* Plumb the --strong option through the dart controller into the VM.
* - Build a strong version of platform.dill for use with the engine.
- Fix a strong mode static error in the assert statement
* Enable asserts when running debug version even in strong mode.
* Use the correct platform dill file for linking when doing the aot builds.
* Fix formatting issue.