Handlify Map::CopyDropDescriptors().

* And contain knowledge better in TransitionArray and DescriptorArray (for example WhitenessWitness is now private to DescriptorArray).
* And remove some factory methods
* And handlify some other things.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/234783002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20686 ce2b1a6d-e550-0410-aec6-3dcde31c8c00