Import/export directives are preserved, and new ones are generated using package syntax using Vijay's logic. This is not yet robust for relative URIs, but is sufficient for our purposes.
Wrapper hoisting is disabled, and various wrapper generation bugs are fixed.
Type name qualification is done more selectively, and more correctly.
Casting is disabled in const contexts, with a severe warning.
Coercions and wrappers now both call into the dart logging runtime, and pass various useful information (currently mostly ignored).
This also adds some preliminary dart codegen tests, and hence includes a number of expected output files in the test/dart_codegen/expect directory.
BUG=
R=jmesserly@google.com, vsm@google.com
Review URL: https://chromereviews.googleplex.com/141427014
John Messerly