Make gmail in chrome the default email application for Yosemite
Solution 1:
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 <<>> on right side of your address bar, click that icon to set default handler.
http://www.ashout.com/complete-guide-to-google-chrome-handlers/