Review request for JDK-8134609: Allow constructors with same prototoype map to share the allocator map

[Hannes Wallnoefer]

Please review JDK-8134609: Allow constructors with same prototoype map 
to share the allocator map:

http://cr.openjdk.java.net/~hannesw/8134609/webrev/

The details for this are a bit tricky, so I added some notes to the jira 
bug:

https://bugs.openjdk.java.net/browse/JDK-8134609?focusedCommentId=13843176&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13843176

Thanks,
Hannes