Called on the UI thread before OnBeforeBrowse in certain limited cases where navigating a new or different browser might be desirable. This includes user-initiated navigation that might open in a special way (e.g. links clicked via middle-click or ctrl + left-click) and certain types of cross-origin navigation initiated from the renderer process (e.g. navigating the top-level frame to/from a file URL). The |browser| and |frame| values represent the source of the navigation. The |target_disposition| value indicates where the user intended to navigate the browser based on standard Chromium behaviors (e.g. current tab, new tab, etc). The |user_gesture| value will be true (1) if the browser navigated via explicit user gesture (e.g. clicking a link) or false (0) if it navigated automatically (e.g. via the DomContentLoaded event). Return true (1) to cancel the navigation or false (0) to allow the navigation to proceed in the source browser's top-level frame.