Generic tests
Generic tests

This adds some checker tests for subtyping generics.  One test checks that generics are invariant in various ways, another checks that raw type subtyping works, and the last test covers multiple raw type subtyping for multiple parameter generics.

For the last test, it's not clear that this is the behavior that we want, but it's what's currently implemented.

BUG=
R=vsm@google.com

Review URL: https://chromereviews.googleplex.com/130137014

dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk