- Now tunnel all descriptor changes through methods on the map
- Renamed CopyDropTransitions to regular Copy since we always "drop transitions" on copy anyway.
- Merged and moved elements transition map creation.

Review URL: https://chromiumcodereview.appspot.com/10780031

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12105 ce2b1a6d-e550-0410-aec6-3dcde31c8c00