Make order of addition the primary order of descriptor arrays.

Make order of addition the primary order of descriptor arrays.

The order by name is maintained as secondary order by using unused bits in the property details.

This is preliminary work towards sharing descriptors arrays.

The change allows us
- to get rid of the LastAdded bits in the map, binding it to the number of valid descriptors for the given map
- to avoid resorting by enumeration index to create the cache
- (maybe in the future, depending on performance) to get rid of the enumeration cache altogether.

Although generally the number_of_descriptors equals the NumberOfOwnDescriptors in the current version, this is preliminary work towards sharing    descriptors, where maps may have more descriptors than are valid for the map.

Committed: https://code.google.com/p/v8/source/detail?r=12385

[Toon Verwaest, 2012-08-22 15:07:09]

PTAL.

[danno, 2012-08-24 15:43:35]

lgtm