Chrome’s chrome://settings/handlers does not seem to allow you to allow handlers such as mailto and webcal as it should, so here’s a work-around

For mailto:
– Make sure you are logged in to Gmail and the active window is your main Gmail page (or nothing will happen).
– Copy/paste this into the address bar:
javascript:navigator.registerProtocolHandler(“mailto”,”https://mail.google.com/mail/?extsrc=mailto&url=%s“,”Gmail”)
– Add the javascript: to the front again if needed, because when you pasted it, Chrome probably trimmed everything before and including the colon. Then hit enter.

It also works for webcal:
– Make sure you are on your Google Calendar page (or nothing will happen).
– Copy/paste this into the address bar:
javascript:navigator.registerProtocolHandler(“webcal”,”https://www.google.com/calendar/render?cid=%s“,”Google Calendar”)
– Add the javascript: to the front again if it got automatically trimmed. Then hit enter.

Source: http://productforums.google.com/forum/#!topic/chrome/sPhxiTQlf4s