Correct iOS GN hermetic support.

build/config/ios/ios_sdk.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/toolchain/toolchain.gni")
+
 declare_args() {
   # SDK path to use. When empty this will use the default SDK based on the
   # value of use_ios_simulator.
   ios_sdk_path = ""
   ios_sdk_name = ""
   ios_sdk_version = ""
   ios_sdk_platform = ""
   ios_sdk_platform_path = ""
   xcode_version = ""
   xcode_build = ""
@@ skipping 61 matching lines @@
 
 if (ios_sdk_path == "") {
   # Compute default target.
   if (use_ios_simulator) {
     ios_sdk_name = "iphonesimulator"
     ios_sdk_platform = "iPhoneSimulator"
   } else {
     ios_sdk_name = "iphoneos"
     ios_sdk_platform = "iPhoneOS"
   }
-  _ios_sdk_result =
-      exec_script("//build/config/mac/sdk_info.py", [ ios_sdk_name ], "scope")
+
+  ios_sdk_info_args = []
+  if (!use_system_xcode) {
+    ios_sdk_info_args += [
+      "--developer_dir",
+      hermetic_xcode_path,
+    ]
+  }
+  ios_sdk_info_args += [ ios_sdk_name ]
+  script_name = "//build/config/mac/sdk_info.py"
+  _ios_sdk_result = exec_script(script_name, ios_sdk_info_args, "scope")
   ios_sdk_path = _ios_sdk_result.sdk_path
   ios_sdk_version = _ios_sdk_result.sdk_version
   ios_sdk_platform_path = _ios_sdk_result.sdk_platform_path
   ios_sdk_build = _ios_sdk_result.sdk_build
   xcode_version = _ios_sdk_result.xcode_version
   xcode_build = _ios_sdk_result.xcode_build
   machine_os_build = _ios_sdk_result.machine_os_build
   if (use_ios_simulator) {
     # This is weird, but Xcode sets DTPlatformBuild to an empty field for
     # simulator builds.
     ios_platform_build = ""
   } else {
     ios_platform_build = ios_sdk_build
   }
 }
 
 if (ios_enable_code_signing && !use_ios_simulator) {
+  find_signing_identity_args = []
+  if (!use_system_xcode) {
+    find_signing_identity_args += [
+      "--developer_dir",
+      hermetic_xcode_path,
+    ]
+  }
+
   # If an identity is not provided, look for one on the host
   if (ios_code_signing_identity == "") {
-    _ios_identities = exec_script("find_signing_identity.py", [], "list lines")
+    _ios_identities = exec_script("find_signing_identity.py",
+                                  find_signing_identity_args,
+                                  "list lines")
     ios_code_signing_identity = _ios_identities[0]
   }
 
   if (ios_code_signing_identity == "") {
     print("Tried to prepare a device build without specifying a code signing")
     print("identity and could not detect one automatically either.")
     print("TIP: Simulator builds don't require code signing...")
     assert(false)
   }
 }