Ensure that all descriptors have a valid enumeration index, and replace NextEnumIndex with LastAdde…

Ensure that all descriptors have a valid enumeration index, and replace NextEnumIndex with LastAdded.

The LastAdded points to the descriptor that was last added to the array. From the descriptor we can deduce the NextEnumerationIndex. This allows us to quickly find the property that we are transitioning to, which is necessary for transition-intensive code, eg JSON parsing.

Committed: https://code.google.com/p/v8/source/detail?r=12042

[Toon Verwaest, 2012-07-09 12:24:35]

PTAL.

[danno, 2012-07-11 14:02:10]

LGTM with comment

http://codereview.chromium.org/10695120/diff/3001/src/objects.cc
File src/objects.cc (right):

http://codereview.chromium.org/10695120/diff/3001/src/objects.cc#newcode6030
src/objects.cc:6030: break;
Verify that none of the elements is higher.

[Toon Verwaest, 2012-07-11 14:23:41]

Addressed comment. Apparently the last value in the descriptor array isn't
always the last added, so now I linearly scan through it.