Makes change_id unsigned

Makes change_id unsigned

Easier this way for clients to track and not worry about overflow.

BUG=none
TEST=none
R=ben@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266793

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266886

[Ben Goodger (Google), 2014-04-28 21:41:23]

It's not that we don't have to worry about overflow, it's that we don't have to
worry about signed overflow. :-)

LGTM

[sky, 2014-04-28 22:47:54]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-04-28 22:48:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/253883005/20001

[commit-bot: I haz the power, 2014-04-28 23:28:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-28 23:28:40]

Try jobs failed on following builders:
  tryserver.chromium on win_chromium_rel

[sky, 2014-04-29 00:15:56]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-04-29 00:16:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/253883005/20001

[commit-bot: I haz the power, 2014-04-29 09:04:10]

Change committed as 266793

[Michael Achenbach, 2014-04-29 09:20:17]

A revert of this CL has been created in
https://codereview.chromium.org/252143003/ by machenbach@chromium.org.

The reason for reverting is: Breaks compile on win builder:
http://build.chromium.org/p/chromium.win/builders/Win%20Builder%20%28dbg%29/b....

[sky, 2014-04-29 14:53:23]

I was reverted as the typedef in the test is bogus now (it'll be needed once I
land the test cleanup patch). I've fixed the test in the latest patchset and
will reland.

[sky, 2014-04-29 14:54:26]

Committed patchset #3 manually as r266886 (presubmit successful).