Add presubmit check for #pragma once.

Add presubmit check for #pragma once.

BUG=none
TEST=git cl presubmit

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=146166

[dcheng, 2012-07-11 05:26:54]

As fun as I think it would be to submit this now, I'll wait for your #pragma
once removal patch to land first.

[awong, 2012-07-11 05:41:06]

LGTM w/ one comment

Thanks...and yeah...I think waiting for the glut of #pragma once removals to go
through first is a good idea.

http://codereview.chromium.org/10704150/diff/1/PRESUBMIT.py
File PRESUBMIT.py (right):

http://codereview.chromium.org/10704150/diff/1/PRESUBMIT.py#newcode371
PRESUBMIT.py:371: 'Do not use #pragma once in header files.\n' +
I don't think you need this plus to concat these strings.  In fact, I think if
you do, you end up making an o(n) copy...

[dcheng, 2012-07-11 05:44:19]

http://codereview.chromium.org/10704150/diff/1/PRESUBMIT.py
File PRESUBMIT.py (right):

http://codereview.chromium.org/10704150/diff/1/PRESUBMIT.py#newcode371
PRESUBMIT.py:371: 'Do not use #pragma once in header files.\n' +
On 2012/07/11 05:41:06, awong wrote:
> I don't think you need this plus to concat these strings.  In fact, I think if
> you do, you end up making an o(n) copy...

Oops, you're right. I copied this from the iostream check so I'll fix that site
as well.