Canonical developer Olivier Tilloy has created a VAAPI-enabled Chromium snap using the Fedora patch (which got Chromium with VAAPI support about 2 weeks ago), and published it in a new candidate/vaapi channel. Thanks to this, Ubuntu and other Linux distributions that can enable Snap support, can easily install Chromium with Video Acceleration API enabled, which should bring smoother video playback, less CPU usage and improved power usage.
Edit: this no longer works. You can install the snap package, but it doesn't have hardware-accelerated video decoding anymore (bug report). Right now the only way to get VAAPI support for a Chromium web browser on Ubuntu is to use the Chromium with VAAPI patches PPA.
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| Chromium VAAPI-enabled snap running in Ubuntu 18.04 - notice the low CPU usage when playing a YouTube video |