This fixes the case where the index passed to {HMaybeGrowElements} used
to derive the new capacity for the elements backing store does not fit
into Smi range. Such an overflow would fail the capacity check and cause
growing to be skipped. Subsequent keyed stores would potentially go out
of bounds.

R=mvstanton@chromium.org
TEST=mjsunit/regress/regress-crbug-686427
BUG=chromium:686427

Review-Url: https://codereview.chromium.org/2686263002
Cr-Commit-Position: refs/heads/master@{#43101}