The code for Chrome for iOS was kept separate from the rest of the Chromium project due to the additional complexity required for the platform. After years of careful refactoring, all of this code is rejoining Chromium and being moved into the open-source repository.
Due to constraints of the iOS platform, all browsers must be built on top of the WebKit rendering engine. For Chromium, this means supporting both WebKit as well as Blink, Chrome’s rendering engine for other platforms. That created some extra complexities which we wanted to avoid placing in the Chromium code base.
According to the company’s blog “Given Chrome’s commitment to open-source code, we’ve spent a lot of time over the past several years making the changes required to upstream the code for Chrome for iOS into Chromium. Today, that upstreaming is complete, and developers can compile the iOS version of Chromium like they can for other versions of Chromium. Development speed is also faster now that all of the tests for Chrome for iOS are available to the entire Chromium community and automatically run any time that code is checked in.”
Check the code here.