find-releases: handle untagged merges

find-releases: handle untagged merges

At the moment, this doesn't work too well for something that was just merged to
45.

[(b912ace...)]scottmg@scottmg:/work/cr/src$ git find-releases 55b4c95889d6a72e52bc72702580a62f04f35777
commit 55b4c95889d6a72e52bc72702580a62f04f35777 was:
  initially in 47.0.2501.0
  merged to undefined (as de54b58d404a0cdf01639ae7260ef10bbb843ed9)
  merged to 46.0.2490.19 (as b4ba1071baaabc92cb5a2ca89e238c478eca0075)

("undefined" being the problem). This is because:

[(b912ace...)]scottmg@scottmg:/work/cr/src$ git name-rev --tags de54b58d404a0cdf01639ae7260ef10bbb843ed9
de54b58d404a0cdf01639ae7260ef10bbb843ed9 undefined

But,

[(b912ace...)]scottmg@scottmg:/work/cr/src$ cat .git/refs/remotes/branch-heads/2454
de54b58d404a0cdf01639ae7260ef10bbb843ed9

So, if name-rev --tags says it's not yet tagged, rather than just printing
'undefined', at least say which branch it was merged to. As in:

[(b912ace...)]scottmg@scottmg:/work/cr/src$ git find-releases 55b4c95889d6a72e52bc72702580a62f04f35777
commit 55b4c95889d6a72e52bc72702580a62f04f35777 was:
  initially in 47.0.2501.0
  merged to branch-heads/2454 [untagged] (as de54b58d404a0cdf01639ae7260ef10bbb843ed9)
  merged to 46.0.2490.19 (as b4ba1071baaabc92cb5a2ca89e238c478eca0075)


R=dpranke@chromium.org,primiano@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=296621

[Dirk Pranke, 2015-09-09 23:00:19]

lgtm

[scottmg, 2015-09-09 23:10:20]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2015-09-09 23:10:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1325233005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1325233005/1

[commit-bot: I haz the power, 2015-09-09 23:15:38]

Committed patchset #1 (id:1) as
http://src.chromium.org/viewvc/chrome?view=rev&revision=296621

[Primiano Tucci (use gerrit), 2015-09-09 23:16:44]

lgtm