MIPS: HInnerAllocatedObject instruction allows hydrogen code to carve up allocated regions into sub objects.

Port r13928 (ff66bd4bcdb580438d96c610bcbe8852bb127908)

BUG=

Review URL: https://codereview.chromium.org/12784003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13985 ce2b1a6d-e550-0410-aec6-3dcde31c8c00