roll GN

up to https://gn-review.googlesource.com/c/gn/+/8920

Change-Id: Ibf69abea267f092fe1bcfed3b7c02a8935223e36
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296705
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

bin/fetch-gn

@@ -24,7 +24,7 @@ with open(gnzip, 'wb') as f:
   pkg = 'linux-amd64' if 'linux'  in sys.platform else \
         'mac-amd64'   if 'darwin' in sys.platform else \
         'windows-amd64'
-  rev = '82d673acb802cee21534c796a59f8cdf26500f53'
+  rev = 'c2859efed0a865637a3c760392fd90585163b44a'
   url = 'https://chrome-infra-packages.appspot.com/dl/gn/gn/{}/+/git_revision:{}'.format(pkg,rev)
   f.write(urlopen(url).read())