Update to Chromium version 82.0.4085.0 (#749737)

- Building on macOS now requires the 10.15 SDK. Xcode 11.3 is recommended as
  Xcode 11.4 is not currently supported (see https://crbug.com/1065146).
- Jumbo build configuration is no longer supported.

Chromium is skipping the M82 release and consequently no CEF 4085 branch will
be created. For details on the Chromium decision see
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/Vn7uzglqLz0/JItlSrZxBAAJ

libcef/browser/native/browser_platform_delegate_native_linux.cc

@@ -258,10 +258,10 @@ void CefBrowserPlatformDelegate::HandleExternalProtocol(const GURL& url) {}
 
 CefEventHandle CefBrowserPlatformDelegateNativeLinux::GetEventHandle(
     const content::NativeWebKeyboardEvent& event) const {
-  if (!event.os_event)
-    return nullptr;
-  return const_cast<CefEventHandle>(
-      static_cast<CefEventHandle>(event.os_event->native_event()));
+  // TODO(cef): We need to return an XEvent* from this method, but
+  // |event.os_event->native_event()| now returns a ui::Event* instead.
+  // See https://crbug.com/965991.
+  return nullptr;
 }
 
 std::unique_ptr<CefMenuRunner>