Implemented folding of constant size allocation followed by dynamic size allocation.
Manually folded allocations (JSArray, JSRegExpResult) are split into two separate allocations.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/304153009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21671 ce2b1a6d-e550-0410-aec6-3dcde31c8c00