Except you can't. Every browser on iOS uses Safari's rendering engine. Chrome/Firefox on iOS are effectively reskinned Safari. This is an apple requirement. The rendering engine being the important part here when talking about standards and such.
It's worse than that, even - IIRC the renderer that other browsers have to use is slower and more limited than the one Safari uses.
So other browsers are effectively reskinned hobbled Safari.
Browsers on iOS can't - they are required (legally, not technologically) to use (a worse version of) Safari's engine. Chrome for iOS is not the browser that the chrome team wants to distribute, it's a browser Apple made that has been customized to the extent that Apple allows it to be customized. What is that if not reskinned?