vm allows generative constructors to return arbitrary expressions.

[DartBot]

This issue was originally filed by fab...@google.com

---

Dart Spec v0.03, section 11.10

"It is a compile-time error if a return statement of the form return e; appears in a generative constructor (7.5.1)."

"A return statement of the form return; is executed by executing the statement return null; if it occurs inside a method, getter, setter or factory; otherwise, the return statement necessarily occurs inside a generative constructor, in which case it is executed by executing return this;"

[DartBot]

This comment was originally written by drfibonacci@google.com

---

Added Triaged label.

[ghost]

Added Fixed label.