As requested in bug 137299, I'm filing this request to explain the larger problem that using a custom protocol handler solves for Chromium: Chromium has its own network stack, which we have always used in Chrome for iOS. Using our own network stack allows us to experiment with, and allows our users to benefit from, improvements in the core networking behaviors in the app. The most obvious example of this is SPDY, which was quite successful, but it is not the only example. Notably, QUIC is a similar development effort that would effectively die for iOS browsers in the short term if Chrome for iOS adopted WKWebView. Having our own network stack also allows customization and experimentation in a variety of other areas: caching behaviors, certificate handling, compression, transcoding unsupported formats (e.g., WebP) on the fly, etc. Absent custom protocol support in WebKit2, or some other way to use a custom network stack, exploration in networking in the context of an iOS browser will become impossible.