fixes https://github.com/dart-lang/dev_compiler/issues/471
Changes here are:
* Analyzer now infers list/map literals
* Analyzer changed how isPotentiallyMutated* APIs work, so we need to track current function
* Another fix to arrow functions. We shouldn't skip generating covariant arg checks. If there were any, we use `=> { block }` form rather than `=> expr` form.
R=vsm@google.com
Review URL: https://codereview.chromium.org/1757343002 .
John Messerly