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

BUG=948286

Change-Id: I85f44622efaf4f018d00046e4fc5dc0757f38539
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1545127
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/DEPS b/DEPS
index 6d91668..e4f2b83 100644
--- a/DEPS
+++ b/DEPS
@@ -36,17 +36,17 @@
 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 @@
                 '-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 @@
     '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.