from the Google Security Blog...
No More Mixed Messages About HTTPS [security.googleblog.com]:

Today we’re announcing that Chrome will gradually start ensuring that https:// pages can only load secure https:// subresources. In a series of steps outlined below, we’ll start blocking mixed content (insecure http:// subresources on https:// pages) by default. This change will improve user privacy and security on the web, and present a clearer browser security UX to users.

these steps will include settings to unblock mixed content, autoupgrading of insecure content, and use of a "Not Secure" chip in the omnibox.