X87: Fix uninitialized FixedArray potentially being left behind by ElementsTransitionGenerator::Generate.

port r24498.

original commit message:
  Fix uninitialized FixedArray potentially being left behind by ElementsTransitionGenerator::Generate.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/643793002

Patch from Chunyang Dai <chunyang.dai@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24508 ce2b1a6d-e550-0410-aec6-3dcde31c8c00