If you find that you are having problems with the RealPlayer Downloader button not appearing on YouTube videos in Chrome, or it appears but does not download the video when you click on it, then the solution is straight forward.
In Downloads option set within RealPlayer Preferences, make sure you have the Chrome option set.
In Chrome, navigate to extensions and disable flash. Now attempt to watch a YouTube video. You should see that the Flash plugin is not available, and that there is a message prompting you to download the latest Flash plugin.
Proceed to download the Flash plugin. Once the plugin has been successfully installed, retry the video. If the video successfully loads, place your cursor over the video, and the RealPlayer Downloader button should appear. Click the button to download the video.
At this point the video should successfully download.