For the PR spin take, see Microsoft Edge: Making the web better through more open source collaboration | Windows Blog; for the Mozilla take, see Goodbye, EdgeHTML | Mozilla blog (lead paragraph: "Microsoft is officially giving up on an independent shared platform for the internet. By adopting Chromium, Microsoft hands over control of even more of online life to Google.").
“Ultimately, we want to make the web-experience better for many different audiences,” explains Joe Belfiore, corporate vice president of Windows. “People using Microsoft Edge (and potentially other browsers) will experience improved compatibility with all web sites, while getting the best-possible battery life and hardware integration on all kinds of Windows devices.”"