No need to go anywhere else in the browser anymore: you only need to click the Cast icon and click the chevron next to "Cast to" in order to see the option under the list of sources. It's only live for some people on the Beta channel at the moment, but you can also force it to show up. Right click on Chrome beta, choose properties and add the command line flag "--enable-features=EnableCastLocalMedia" to switch the feature on. If you cast a lot of files from your PC, this could make the process of opening videos less tedious, though you'll have to wait for a wider release if you don't want to play with the browser's beta offerings.