Allow target_ref to be modified by subsequent patchsets with logging
Allow target_ref to be modified by subsequent patchsets with logging

The motivation of this CL are changes that are created by tracking "refs/pending/heads/lkcr".
Eg: https://codereview.chromium.org/812793002
A possible workflow would be to run "git reparent-branch origin/master" or "git branch --set-upstream-to origin/master" on such CLs and reupload when ready to commit.

BUG=435702
NOTRY=true
TBR=jrobbins

Review URL: https://codereview.chromium.org/806373005

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra