Add missing comma to third_party.gyp

Add missing comma to third_party.gyp

A reference to nonstd_unique_ptr.h was added with
https://codereview.chromium.org/1091283002 but a comma is missing
after it. This causes this string to be concatenated with the next,
leading to broken sources. This went unnoticed by the build due to
the fact that the affected sources are both headers, but they should
be properly separated.

R=brucedawson@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/8e1b60824d079546c8cc3f0e3d9fa0ea9fa980fa

[bungeman-chromium, 2015-05-27 20:48:56]

The CQ bit was checked by bungeman@chromium.org to run a CQ dry run

[bungeman-chromium, 2015-05-27 20:50:38]

bungeman@chromium.org changed reviewers:
+ brucedawson@chromium.org

[brucedawson, 2015-06-01 18:03:08]

lgtm

Thanks for catching this. I CCed Tom to make sure he knows also.

It seems that build\gyp_pdfium should detect and warn or fail on missing files
(which would have caught this). Lack of this check means that Chrome's .gyp
files have references to 20-30 nonexistent files. But, that is a separate issue.

[Tom Sepez, 2015-06-01 18:06:43]

Yeah, I can't type. LGTM.

[bungeman-chromium, 2015-06-01 18:24:03]

On 2015/06/01 18:06:43, Tom Sepez wrote:
> Yeah, I can't type. LGTM.

It looks like one normally just 'git cl land's changes to pdfium, but it's
telling my that git access is forbidden. I'm not immediately finding any
documentation on how to land. If there's something simple I can do to land this,
let me know. Otherwise, feel free to land this yourself if that's easier.

[brucedawson, 2015-06-01 21:42:35]

I'll land it, and merge to the other branch.

[brucedawson, 2015-06-01 21:44:58]

Committed patchset #1 (id:1) manually as
8e1b60824d079546c8cc3f0e3d9fa0ea9fa980fa (presubmit successful).

[Tom Sepez, 2015-06-01 23:26:52]

tsepez@chromium.org changed reviewers:
+ tsepez@chromium.org

[Tom Sepez, 2015-06-01 23:26:53]

lgtm