MIPS: Swapped transition array and descriptor array.

MIPS: Swapped transition array and descriptor array.

Port r12298 (7b39ef67)

Original commit message:
Now a map points to a transition array which contains the descriptor array. The descriptor array is now immutable. The next step is to share the descriptor array with all back-pointed maps as long as there is a single line of extension. Maps that require a descriptor array but don't need transitions will still need a pseudo-empty transition array to contain the descriptor array.

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=12319

[Toon Verwaest, 2012-08-16 11:42:12]

LGTM. Landing.