After you make sure the Google Chrome Setting to "Allow sites to ask to become default handlers for protocols (recommended)" is turned on and if you do not see mail.google.com set as a default handle you need to close chrome and open it again and open gmail. Gmail will check your chrome settings to see if it is the default mail handler. If it is not, you will see a message like this in the URL bar. 
Click ALLOW and you are all set!