The maximum indexed element size is maxUint32-1, not maxUint32, because
the maximum length of elements is maxUint32. This patch tweaks the limit
to switch to named properties as appropriate.

BUG=v8:4516
LOG=Y
R=adamk

Review URL: https://codereview.chromium.org/1431503002

Cr-Commit-Position: refs/heads/master@{#31809}