Merged r16346, r16355 into trunk branch.

Added allocation folding support for old space allocations.

Filler sizes have to be Smis, fix x64 breakage.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23545008

git-svn-id: https://v8.googlecode.com/svn/trunk@16368 ce2b1a6d-e550-0410-aec6-3dcde31c8c00