Determine behavior when writeToParcel is already implemented.

[JakeWharton]

What should the behavior be when writeToParcel is already implemented? Fail? No-op? Emit only the describeContents method (and then what happens if this is implemented too)?

[rharter]

With standard AutoValue, anything you implement is not overridden so that your custom implementation is executed. I would expect this would apply to writeToParcel as well.

In the case of both having been implemented by the user, I guess we can change applicable() to return false, since no implementation is needed, assuming we have that information early enough.

[JakeWharton]

There's also the CREATOR to consider here which would also need to be present.