The idea behind the iOS Web Debugger tool was to make it easier for web developers to test out their webpages and webapps on the fly. Microsoft explains:
"When developing websites running locally, it’s a cumbersome process to enable mobile devices access your local development server, which usually is a HTTP server running on localhost. To make this easier, platforms like Android supports port-forwarding natively, but iOS doesn’t support this. So we found a way to emulate port forwarding by adding the option to start an instance of localtunnel, that behind the scenes creates HTTP tunnel from your local computer to the public internet for the specified tunnelPort property. This HTTP tunnel is then used by the iOS device to get access to your local development server, just as any other public website."
To connect the Visual Studio debugging library to an iOS device, the new tool takes advantages of the ios-webkit-debug-proxy and ios-webkit-debug-proxy-win32 open source projects. They allow for communication with iOS devices over USB through the WebKit Remote Debugging Protocol.
You can get the tool as an extension for Visual Studio here. For information on how to use the tool can be found over on GitHub.