void check(TypeMirror type) {
      type.accept(this, new TypeMirrorSet());
    }
Check that the return type and parameter types of the given method are all defined, and arrange
to defer processing until the next round if not.

@throws MissingTypeException if the return type or a parameter type of the given method is
    undefined
value/src/main/java/com/google/auto/value/processor/MissingTypes.java