The existing code just used timestamps. The new code uses more fields
    when timestamps are equal.

	Revised to shorten code per reviewer comments.

Change-Id: Ibd0824d0acd7644484d536b1a754a0da156fac3d
Reviewed-on: https://go-review.googlesource.com/113721Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>