Add a mac_toolchain update DEP. Update use_system_xcode to match Chrome.

.gn

@@ -7,8 +7,8 @@
 # As a result this file will only affect stand-alone ANGLE builds,
 # not chromium builds.
 
-import("//dotfile_settings.gni")
 import("//build/dotfile_settings.gni")
+import("//dotfile_settings.gni")
 
 # Location of the build configuration file.
 buildconfig = "//build/config/BUILDCONFIG.gn"
@@ -34,6 +34,7 @@ exec_script_whitelist = angle_dotfile_settings.exec_script_whitelist +
                           "//build/config/win/BUILD.gn",
                           "//build/config/win/visual_studio_version.gni",
                           "//build/gn_helpers.py",
+                          "//build_overrides/build.gni",
                         ]
 
 default_args = {

DEPS

@@ -36,17 +36,17 @@ vars = {
 deps = {
 
   '{angle_root}/build': {
-    'url': '{chromium_git}/chromium/src/build.git@16bafea184ed656b9ec19c0dd18447d08464bd53',
+    'url': '{chromium_git}/chromium/src/build.git@a660b0b9174e3a808f620222017566e8d1b2669b',
     'condition': 'not build_with_chromium',
   },
 
   '{angle_root}/buildtools': {
-    'url': '{chromium_git}/chromium/src/buildtools.git@62f9eb0d64d6bf48f620b8233d9f7a1dc07f8414',
+    'url': '{chromium_git}/chromium/src/buildtools.git@459baaf66bee809f6eb288e0215cf524f4d2429a',
     'condition': 'not build_with_chromium',
   },
 
   '{angle_root}/testing': {
-    'url': '{chromium_git}/chromium/src/testing@71baa9533c1d21f99dfa8c9e6ca5c1db5f9566bd',
+    'url': '{chromium_git}/chromium/src/testing@083d633e752e7a57cbe62a468a06e51e28c49ee9',
     'condition': 'not build_with_chromium',
   },
 
@@ -217,43 +217,6 @@ hooks = [
                 '-s', '{angle_root}/buildtools/linux64/clang-format.sha1',
     ],
   },
-  # Pull GN binaries using checked-in hashes.
-  {
-    'name': 'gn_win',
-    'pattern': '.',
-    'condition': 'host_os == "win" and not build_with_chromium',
-    'action': [ 'download_from_google_storage',
-                '--no_resume',
-                '--platform=win32',
-                '--no_auth',
-                '--bucket', 'chromium-gn',
-                '-s', '{angle_root}/buildtools/win/gn.exe.sha1',
-    ],
-  },
-  {
-    'name': 'gn_mac',
-    'pattern': '.',
-    'condition': 'host_os == "mac" and not build_with_chromium',
-    'action': [ 'download_from_google_storage',
-                '--no_resume',
-                '--platform=darwin',
-                '--no_auth',
-                '--bucket', 'chromium-gn',
-                '-s', '{angle_root}/buildtools/mac/gn.sha1',
-    ],
-  },
-  {
-    'name': 'gn_linux64',
-    'pattern': '.',
-    'condition': 'host_os == "linux" and not build_with_chromium',
-    'action': [ 'download_from_google_storage',
-                '--no_resume',
-                '--platform=linux*',
-                '--no_auth',
-                '--bucket', 'chromium-gn',
-                '-s', '{angle_root}/buildtools/linux64/gn.sha1',
-    ],
-  },
   {
     'name': 'sysroot_x86',
     'pattern': '.',
@@ -275,6 +238,13 @@ hooks = [
     'condition': 'checkout_win and not build_with_chromium',
     'action': ['python', '{angle_root}/build/vs_toolchain.py', 'update', '--force'],
   },
+  {
+    # Update the Mac toolchain if necessary.
+    'name': 'mac_toolchain',
+    'pattern': '.',
+    'condition': 'checkout_mac and not build_with_chromium',
+    'action': ['python', '{angle_root}/build/mac_toolchain.py'],
+  },
 
   {
     # Note: On Win, this should run after win_toolchain, as it may use it.

build_overrides/build.gni

 # Copyright (c) 2017 The ANGLE Project Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
-build_with_chromium = false
-ignore_elf32_limitations = true
-linux_use_bundled_binutils_override = false
-use_system_xcode = true
+
+declare_args() {
+  build_with_chromium = false
+  ignore_elf32_limitations = true
+  linux_use_bundled_binutils_override = false
+
+  use_system_xcode = ""
+}
+
+if (host_os == "mac" && use_system_xcode == "") {
+  _result = exec_script("//build/mac/should_use_hermetic_xcode.py",
+                        [ target_os ],
+                        "value")
+
+  assert(_result != 2,
+         "Do not allow building targets with the default" +
+             "hermetic toolchain if the minimum OS version is not met.")
+  assert(_result != 3,
+         "iOS does not support building with a hermetic toolchain. " +
+             "Please install Xcode.")
+
+  use_system_xcode = _result != 1
+}