Improve the sort documentation slightly.

Make it a little clearer when ClassCastException can be thrown.

Bug: 10491028

(cherry picked from commit 35def4c9d5fb52e0eb2cb4fa7d8d10618d7e8baa)

Change-Id: I421fb03e8a58fdfebce86f434bf8813075d9bf2f
2 files changed