Correct iOS GN hermetic support.

build/config/ios/find_signing_identity.py

Index: build/config/ios/find_signing_identity.py
diff --git a/build/config/ios/find_signing_identity.py b/build/config/ios/find_signing_identity.py
index 9c3d493d541678b07330ee1863266637b8111a70..16dd523c516ea0565092a18709b48af64e49b86e 100644
--- a/build/config/ios/find_signing_identity.py
+++ b/build/config/ios/find_signing_identity.py
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import argparse
+import os
 import subprocess
 import sys
 import re
@@ -32,4 +34,11 @@ def FindValidIdentity():
 
 
 if __name__ == '__main__':
+  parser = argparse.ArgumentParser('codesign iOS bundles')
+  parser.add_argument('--developer_dir', required=False,
+                      help='Path to Xcode.')
+  args = parser.parse_args()
+  if args.developer_dir:
+    os.environ['DEVELOPER_DIR'] = args.developer_dir
+
   print FindValidIdentity()