Make gmail in chrome the default email application for Yosemite
To Set default protocol handler in your chrome browser, visit any web app or website which support protocol handlers (For ex: Gmail for mailto:, Google Calendar for webcal: ) and you’ll see Protocol handler icon &lt;&lt;>> on right side of your address bar, click that icon to set default handler.

http://www.ashout.com/complete-guide-to-google-chrome-handlers/