Fix for 350887: CHECK failure on new_length->IsSmi()

In ElementsAccessorBase::SetLengthImpl for a dictionary array, we try to
optimize setting array length if the new length is a smi. However, we
refuse to set an array length to less than the index of the highest
non-configurable array element. This index may be outside of smi range.

Handle this case accordingly.

BUG=350887
LOG=N
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/194803002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19787 ce2b1a6d-e550-0410-aec6-3dcde31c8c00