Fix harmless warning in setup_third_party

Fix harmless warning in setup_third_party that was causing all
of the forwarding headers for webkit to be reported as missing.

R=tony@chromium.org
BUG=107444
TEST="missing file" warnings gone from build.webkit.org win bots

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=114519

[tony, 2011-12-14 00:13:13]

I agree that the warning is harmless, but it's a bug in gyp.  I posted a patch
to fix it here:
http://codereview.chromium.org/8937016/

[Dirk Pranke, 2011-12-14 00:14:21]

Oh, okay.

-- Dirk

On Tue, Dec 13, 2011 at 4:13 PM,  <tony@chromium.org> wrote:
> I agree that the warning is harmless, but it's a bug in gyp.  I posted a
> patch
> to fix it here:
> http://codereview.chromium.org/8937016/
>
>
> http://codereview.chromium.org/8933019/

[tony, 2011-12-14 19:45:00]

Mark tells me that this behavior is intentional.  Another option is to single
quote each filename.  Replacing with forward slash seems fine too.  In either
case, this deserves a comment.

With a comment, LGTM

[Dirk Pranke, 2011-12-14 23:01:34]

On 2011/12/14 19:45:00, tony wrote:
> Mark tells me that this behavior is intentional.  Another option is to single
> quote each filename.  Replacing with forward slash seems fine too.  In either
> case, this deserves a comment.
> 
> With a comment, LGTM

Okay, will add a comment and land.