Review request for JDK-8006950

[Hannes Wallnoefer]

Please review webrev for JDK-8006950: 
http://cr.openjdk.java.net/~hannesw/8006950/

The gist of this is that we can omit calling ScriptObject.setProto() in 
constructors of Nasgen-processed  classes if we know the prototype has 
been set correctly in the object's $nasgenmap$ field. This is because 
Nasgen inserts $nasgenmap$ to all calls to zero-arg ScriptObject 
super-constructor. Also, prototype properties of native ES constructors 
are non-writable and non-configurable.

The patch contains an incomplete array microbenchmark (only array 
creation covered so far), most of which now is roughly 3x faster.

Hannes