This allows sloppy arguments objects to be allocated by the generic
Heap::AllocateJSObjectFromMap allocation function. An empty elements
backing store for such objects is provided. This is needed in order to
materialize such objects without access to a specific native context.

R=bmeurer@chromium.org
TEST=mjsunit/regress/regress-crbug-613919
BUG=chromium:613919

Review-Url: https://codereview.chromium.org/2014343004
Cr-Commit-Position: refs/heads/master@{#36547}