The stub used to check the length of the JS array to see if
there's a need to duplicate the elements backing store. This
way it will not duplicate the elements array when going from
double to object even if the elements array is not the empty
fixed array. Later on it will then store pointers into a
FixedDoubleArray.

The native code stub used to check whether elements points to
the empty_fixed_array singleton instead of testing the length.
The Hydrogen stub does that as well now.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/19289009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15701 ce2b1a6d-e550-0410-aec6-3dcde31c8c00