UIWebBroswerView has gap from top of UIWebView

I have a UIWebView which is taking up a whole view in my ViewController, which you can see here:

What I don't understand, is when I run my app, the contents of my UIWebView does not fill up the whole screen, you can see this here, where I first show the extent of the UIWebView (it is indeed taking up the whole screen):

And then here, where I show the extend of the UIWebBrowserView (which seems to have a gap from the top of the UIWebView).

Does anyone know why the UIWebBrowserView has a gap from the top of the UIWebView?

I think this happens because of UIViewController's ScrollView Inset Property. Default value for adjustScrollViewInset is True.

Select ViewController and go to Attribute Inspector Tab. Uncheck Adjust Scroll View Insets option.