Review request for JDK-8035948 - Redesign property listeners for shared classes

[Hannes Wallnoefer]

Please review JDK-8035948 - Redesign property listeners for shared classes:

http://cr.openjdk.java.net/~hannesw/8035948/

This prepares property maps and property listeners to work better with 
classes that are reused between JS environments. The central ideas are:

  - Reuse property maps between globals in order to minimize polymorphism.
  - Use SoftReferences for property map history to avoid memory leaks
  - Redesign property listeners to be attatched to property maps only 
since ScriptObjects are specific to one JS environment.
  - Reduce number of property listeners by only creating them when 
needed (when a callsite accesses an inherited property).
  - Reduce number of prototype history lookups in property maps by using 
a unique combination of prototype/property maps from the start.

Actual class sharing functionality is coming in a later webrev. Let me 
know if you have any questions about this.

Hannes