After https://chromium-review.googlesource.com/c/chromium/src/+/881836 lands, we will swap BrowsingInstances on certain browser-initiated navigations, such as via the omnibox or bookmarks.  As a followup, we might want to provide a ContentBrowserClient method to allow content/ embedders to override this behavior, if it turns out that they need to keep scripting relationships between tabs even after a browser-initiated navigation.  This would be something checked by RenderFrameHostManager::IsBrowsingInstanceSwapAllowedForPageTransition(), and would allow embedders to return false.  Something similar might be used to deal with process-per-tab issue 717459 as well.  Filing this so we don't lose track of this (thanks to nasko@ for the idea).