Use bundled SDK 10.12 toolchain for Mac and iOS.

DEPS

 # This file contains dependencies for WebRTC.
 
 vars = {
   'chromium_git': 'https://chromium.googlesource.com',
   'chromium_revision': 'f156b499f700f849d110801e8a303c00c98ae5bc',
   'boringssl_git': 'https://boringssl.googlesource.com',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling swarming_client
   # and whatever else without interference from each other.
   'swarming_revision': '42721e128da760b345ab60d7cf34e300269112d7',
@@ skipping 352 matching lines @@
     'pattern': '.',
     'action': ['python', 'src/build/linux/sysroot_scripts/install-sysroot.py',
                '--running-as-hook'],
   },
   {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'src/build/vs_toolchain.py', 'update'],
   },
+  {
+    # Update the Mac toolchain if necessary.
+    'name': 'mac_toolchain',
+    'pattern': '.',
+    'action': ['python', 'src/build/mac_toolchain.py'],
+  },
   # Pull binutils for linux, enabled debug fission for faster linking /
   # debugging when used with clang on Ubuntu Precise.
   # https://code.google.com/p/chromium/issues/detail?id=352046
   {
     'name': 'binutils',
     'pattern': 'src/third_party/binutils',
     'action': [
         'python',
         'src/third_party/binutils/download.py',
     ],
@@ skipping 160 matching lines @@
       ],
     },
   ],
 }
 recursedeps = [
   # buildtools provides clang_format, libc++, and libc++abi.
   'src/buildtools',
   # android_tools manages the NDK.
   'src/third_party/android_tools',
 ]