Add support for type references to AccessSemantics.

We now handle references to toplevel classes, e.g.:

  class C {}
  Type t = C;

And references to type parameters, e.g.:

  class C<T> {
    f() {
      Type t = T;
    }
  }

R=scheglov@google.com

Review URL: https://codereview.chromium.org//710163002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41643 260f80e4-7a28-3924-810f-c04153c831b5
Adds extra validation to code collection test.

R=iposva@google.com

Review URL: https://codereview.chromium.org//710093002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41644 260f80e4-7a28-3924-810f-c04153c831b5