Review request for JDK-8022731: NativeArguments has wrong implementation of isMapped()

[Hannes Wallnoefer]

Please review JDK-8022731: NativeArguments has wrong implementation of 
isMapped():

http://cr.openjdk.java.net/~hannesw/8022731/
This also makes NativeArguments a bit slimmer, avoiding allocation of 
new ArrayData in the constructor and overriding a few dozen ScriptObject 
methods.

Thanks,
Hannes