Minor bugfix in building inlined Array: bad argument to JSArrayBuilder.

An HConstant pointing to a Cell rather than an AllocationSite
was passed. The argument wasn't used because of fortuitous
flags. An assert was added to protect the argument.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/141533003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18666 ce2b1a6d-e550-0410-aec6-3dcde31c8c00