Add ToObject call in Array.prototype.sort

Add ToObject call in Array.prototype.sort

The spec says ToObject is called on the receiver, and this is
observable if you call sort on a primitive. This patch trivially
adds the call and a test.

BUG=v8:4125
R=adamk
LOG=Y

Review URL: https://codereview.chromium.org/1178193004

Cr-Commit-Position: refs/heads/master@{#28972}