RefMap tracks its number of live Ref instances in the 'live' member. However, when a reference was removed and later added, 'live' wasn't updated accordingly. Fix and add a test. Change-Id: I806e17ea0319d76db4d07b5f8d9107b146ee80db Reviewed-on: https://go-review.googlesource.com/19975 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>