Force HTTP/2 With Chrome or Safari
HTTP/2 over TLS and HTTP/2 over TCP have been defined as 2 different protocols, identified respectively by h2 and h2c.
Chrome supports h2 only at this time.
If you have a server that implements only h2c, the easiest way to connect Chrome to it is to use a reverse proxy such a nghttpx in HTTP/2 bridge mode in front of your server
As far as I know this is most likely a browser-wide setting. In chrome you can enable SPDY4, see chrome://flags
As far as safari goes support has been added since version 8.
In the end it's all about the knowing whether or not you speak the same language as the server. If you are using http you can check this by using the Upgrade header. There are some plugins out there you can use with chrome to give you an indication of whether or not the address your visiting supports http/2.
For more info on the http/2 protocol itself you should check out https://http2.github.io/http2-spec/#starting