Move left and right trimming of FixedArray into Heap.

R=hpayer@chromium.org
BUG=v8:3231
LOG=n

Review URL: https://codereview.chromium.org/200443004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22858 ce2b1a6d-e550-0410-aec6-3dcde31c8c00