[presubmit] Use bin/gn rather than depot_tools gn

Change-Id: I649f07e036f184e6dbb3a335bdd979dedea27ec8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270876
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index a80c762..0e06a17 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -169,11 +169,12 @@
       continue
 
     gn = 'gn.bat' if 'win32' in sys.platform else 'gn'
+    gn = os.path.join(input_api.PresubmitLocalPath(), 'bin', gn)
     cmd = [gn, 'format', '--dry-run', f.LocalPath()]
     try:
       subprocess.check_output(cmd)
     except subprocess.CalledProcessError:
-      fix = 'gn format ' + f.LocalPath()
+      fix = 'bin/gn format ' + f.LocalPath()
       results.append(output_api.PresubmitError(
           '`%s` failed, try\n\t%s' % (' '.join(cmd), fix)))
   return results