[iOS] Fix compilation of official build with Xcode 8.

build/config/mac/mac_sdk.gni

 # Copyright 2014 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/config/chrome_build.gni")
 
 # See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
 # We can drop the rtc_require_mac_10_7_deployment flag when Chromium
 # also requires a 10.7 deployment target.
 import("//build_overrides/build.gni")
 
 declare_args() {
   # Minimum supported version of the Mac SDK.
   mac_sdk_min = mac_sdk_min_build_override
 
   # Minimum supported version of OSX.
   mac_deployment_target = mac_deployment_target_build_override
 
   # Path to a specific version of the Mac SDK, not including a backslash at
   # the end. If empty, the path to the lowest version greater than or equal to
   # mac_sdk_min is used.
   mac_sdk_path = ""
 
   # The SDK name as accepted by xcodebuild.
   mac_sdk_name = "macosx"
 }
 
+# Check that the version of macOS SDK used is the one requested when building
+# a version of Chrome shipped to the users. Disable the check if building for
+# iOS as the version macOS SDK used is not relevant for the tool build for the
+# host (they are not shipped) --- this is required as Chrome on iOS is usually
+# build with the latest version of Xcode that may not ship with the version of
+# the macOS SDK used to build Chrome on mac.
+# TODO(crbug.com/635745): the check for target_os should be replaced by a
+# check that current_toolchain is default_toolchain, and the file should
+# assert that current_os is "mac" once this file is no longer included by
+# iOS toolchains.
+_verify_sdk = is_chrome_branded && is_official_build && target_os != "ios"
+
 find_sdk_args = [ "--print_sdk_path" ]
-if (is_chrome_branded && is_official_build) {
+if (_verify_sdk) {
   find_sdk_args += [
     "--verify",
     mac_sdk_min,
     "--sdk_path=" + mac_sdk_path,
   ]
 } else {
   find_sdk_args += [ mac_sdk_min ]
 }
 
 # The tool will print the SDK path on the first line, and the version on the
@@ skipping 29 matching lines @@
       "          either upgrade Xcode to the latest version or install the Mac OS X")
   print(
       "          $mac_sdk_min_build_override SDK. For more information, see https://crbug.com/620127.")
   print()
   print(" Current SDK Version:   $mac_sdk_version")
   print(" Current Xcode Version: $xcode_version ($xcode_build)")
   print(
       "********************************************************************************")
   assert(false, "SDK is incompatible with Xcode")
 }