On the Chrome Blog, Director of Engineering Marc Pawliger announced that Google will continue to support Chrome on Windows XP until April 2016, extending its life for four additional months.
In addition to Windows XP, Windows Vista, and Mac OS X 10.6, 10.7, and 10.8 will also lose support in April. "Chrome will continue to function on these platforms but will no longer receive updates and security fixes," said Pawliger. Ostensibly, the reason for dropping these platforms is that the OS in question is no longer supported by the company. However, Windows Vista will enjoy official support through April 2017.
For now, Firefox has not announced any plans to cease support on Windows XP, so that may be an option for those that want to keep their browser updated on that OS. IE8 will lose its last glimmer of support on January 12, 2016. On that day, Windows Vista will only have support for IE9.
On Hacker News, user ivraatiems was discouraged about the Mac OS versions losing support:
I'm disappointed about OS X 10.7 and 10.8, because many users with older (but still perfectly functional!) Mac hardware are stuck on those versions 4-5 years after their release because Apple won't extend support for newer OS X versions to that hardware. Apple also refuses to provide a way to upgrade a system to the maximum OS X version it supports; it's a huge hassle to do so.
In April of 2015, Google said that Chrome support on Windows XP would last until the end of 2015. They said that the lack of OS support forced them do drop support:
At the operating system level, computers running XP are inherently in danger of being infected by malware and viruses, making it increasingly difficult for Chrome to provide a secure browsing environment. That’s why we strongly encourage everyone to update to a supported, secure operating system.