Chroms of iOS is a re-skinned Safari WebView[1]. They just put a front-end on it with their added on features. Apple entirely controls the browser and what's allowed, disallowed, supported, etc. For example, Google's SPDY protocol wasn't supported until Safari 8[2], and probably then because much of what SPDY entailed was adopted as HTTP/2.

1: https://developer.chrome.com/multidevice/ios/overview

2: http://caniuse.com/#feat=spdy