Add presubmit for gn formatting

Add presubmit for gn formatting

If you want. I'll probably add it to chrome next week sometime.

(Includes buildtools roll for gn binary.)

R=jamesr@chromium.org,eseidel@chromium.org
BUG=348474

[jamesr, 2014-12-06 00:54:46]

We normally keep the DEPS hashes completely in sync with chrome's, so if we take
this then do another roll from chrome we'll have to remember to keep the
buildtools_revision line ahead or we might blow away the line (and break the
presubmit).  I think I'd prefer to wait for the buildtools roll to land in
chrome then add the presubmit

(I am really excited about the contents of the presubmit just worried about the
mechanics)

[scottmg, 2014-12-06 00:57:41]

OK, it just rolled into chrome.

I don't want to do the full roll in case there's other things that I don't
understand/etc., so I'll let you just add the presubmit whenever is the right
time then.

[jamesr, 2014-12-06 00:59:39]

OK cool.  I'll do a roll then land the PRESUBMIT.py change from here. 
*normally* the roll is painless but every now and then there's a tricky API
change upstream that can be annoying.

[jamesr, 2014-12-08 22:13:49]

Landed (w/ roll) at
https://chromium.googlesource.com/external/mojo/+/d2015d9f67dc968437fd3dc578d...

[scottmg, 2014-12-08 22:14:53]

On 2014/12/08 22:13:49, jamesr wrote:
> Landed (w/ roll) at
>
https://chromium.googlesource.com/external/mojo/+/d2015d9f67dc968437fd3dc578d...

Thanks!

(It's on in chromium now too.)