This makes super calls name-based (no target) and add direct calls with
both receiver and explicit target.
Super call resolution translates the name-based super calls into direct
calls after they have been cloned into the mixin application.
For JS backends, it should suffice to clone mixed-in methods that
contain super calls, but that transformation is not part of this CL.
This also adds a --target option to dartk designating the target to
which the kernel IR should be specialized. The new transformation
is run when --target=vm.
BUG=
R=kmillikin@google.com
Review URL: https://chromereviews.googleplex.com/486537013 .
Asger Feldthaus