Web Browser Project: Expand WebView when SearchBar is hidden (Xcode, Swift 3)

I am making a web browser for my iPhone. So far, it consists of a SearchBar on top, a WebView in the middle, and a ToolBar on bottom. I have added a button in the ToolBar that when clicked toggles the SearchBar on/off.

Now, what I want to do is get the WebView to expand upwards where the SearchBar was (when the SearchBar is hidden via button). How can I achieve this?

Thanks in advance, Jon