Fix multi-rename empty branch detection.

Fix multi-rename empty branch detection.

This changes the 'empty' branch detection to compare the commit trees instead
of the commit hashes. This avoids empty-branch detection when you have multiple
renames on the branch that end up canceling eachother out. Previously you'd
end up with the rename-commits, in order, in your rebased branch, even though
when you run `git upstream-diff` you get nothing.

R=agable@chromium.org, jochen@chromium.org, vadimsh@chromium.org
BUG=438208
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=297849

[agable, 2015-12-04 19:06:48]

lgtm

[iannucci, 2015-12-04 19:07:27]

On 2015/12/04 at 19:03:33, iannucci wrote:
> 

It's not just renames, actually, it's any series of changes which cancel each
other out that rebase somehow doesn't squash.

[iannucci, 2015-12-04 19:07:35]

The CQ bit was checked by iannucci@chromium.org

[commit-bot: I haz the power, 2015-12-04 19:07:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1497313002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1497313002/1

[commit-bot: I haz the power, 2015-12-04 19:09:32]

Description was changed from

==========
Fix multi-rename empty branch detection.

This changes the 'empty' branch detection to compare the commit trees instead
of the commit hashes. This avoids empty-branch detection when you have multiple
renames on the branch that end up canceling eachother out. Previously you'd
end up with the rename-commits, in order, in your rebased branch, even though
when you run `git upstream-diff` you get nothing.

R=agable@chromium.org, jochen@chromium.org, vadimsh@chromium.org
BUG=438208
==========

to

==========
Fix multi-rename empty branch detection.

This changes the 'empty' branch detection to compare the commit trees instead
of the commit hashes. This avoids empty-branch detection when you have multiple
renames on the branch that end up canceling eachother out. Previously you'd
end up with the rename-commits, in order, in your rebased branch, even though
when you run `git upstream-diff` you get nothing.

R=agable@chromium.org, jochen@chromium.org, vadimsh@chromium.org
BUG=438208

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=297849
==========

[commit-bot: I haz the power, 2015-12-04 19:09:33]

Committed patchset #1 (id:1) as
http://src.chromium.org/viewvc/chrome?view=rev&revision=297849