What browser is using Corona SDK for the native WebView?
I presume for iOS it is using an Objective C WebView which should use Safari, and for Android it's using Chrome, but I haven't been able to find any reference to it.
I don't know abut Android But iOS UIWebView is not safari that is sure.
You can rad some difference here : UIWebView and Safari comparison
One more article about this : Apple confirms some WebKit optimizations unavailable to iOS Apps
iOS 8 give new WebView named WKWebView One good article about this is here : NSHipster : WKWeb​View
But I don't know that Corona is going to use WKWebView or not.