Helper method to ensure all ChromiumWebBrowser instances have been
closed/disposed, should be called before Cef.Shutdown.
Disposes all remaining ChromiumWebBrowser instances
then waits for CEF to release its remaining CefBrowser instances.
Finally a small delay of 50ms to allow for CEF to finish it's cleanup.
Should only be called when MultiThreadedMessageLoop = true;
(Hasn't been tested when when CEF integrates into main message loop).
CefSharp.Core (in CefSharp.Core.dll) Version: 184.108.40.206
public static void WaitForBrowsersToClose()