Update to Chromium version 86.0.4240.0 (#800218)

- CefURLRequest::Create is no longer supported in the renderer process
  (see https://crbug.com/891872). Use CefFrame::CreateURLRequest instead.
- Mac platform definitions have been changed from `MACOSX` to `MAC`
  (see https://crbug.com/1105907) and related CMake macro names have
  been updated. The old `OS_MACOSX` define is still set in code and CMake
  for backwards compatibility.
- Linux ARM build is currently broken (see https://crbug.com/1123214).

tools/gclient_hook.py

@@ -21,7 +21,7 @@ src_dir = os.path.abspath(os.path.join(cef_dir, os.pardir))
 if sys.platform == 'win32':
   platform = 'windows'
 elif sys.platform == 'darwin':
-  platform = 'macosx'
+  platform = 'mac'
 elif sys.platform.startswith('linux'):
   platform = 'linux'
 else: