A blog post from the Chrome team in September provides the story:
That’s why Chrome will start the process of sunsetting SHA-1 (as used in certificate signatures for HTTPS) with Chrome 39 in November. HTTPS sites whose certificate chains use SHA-1 and are valid past 1 January 2017 will no longer appear to be fully trustworthy in Chrome’s user interface.
Notice that the certificate expires September 2017 and that it is signed and hashed with SHA-1.