Teach bisect script to resolve Cr-Commit-Positions.

Teach bisect script to resolve Cr-Commit-Positions.

Multiple --grep args to git log use the OR operation. So this patch supports
both old SVN revisions as well as newer commit positions.

BUG=407291
NOTRY=True

Committed: https://crrev.com/8f9ae0d22117f06f924f82bf4a484d43a99b4dd5
Cr-Commit-Position: refs/heads/master@{#291757}

[prasadv, 2014-08-25 20:30:30]

lgtm

[tonyg, 2014-08-25 20:47:31]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-08-25 20:48:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tonyg@chromium.org/470803009/1

[commit-bot: I haz the power, 2014-08-25 20:50:04]

Committed patchset #1 (1) as b4a8bc8459720b7cc13d942350dbfc04a1a08af2

[commit-bot: I haz the power, 2014-09-10 02:37:25]

Patchset 1 (id:??) landed as
https://crrev.com/8f9ae0d22117f06f924f82bf4a484d43a99b4dd5
Cr-Commit-Position: refs/heads/master@{#291757}