WebContentsImpl::CreateNewWindow depends on WebContentsDelegate::AddNewContents for the |params.opener_suppressed | case.  GuestViewBase doesn't implement AddNewContents.  Let's use this bug to track down if this is okay.

Some guest views might not care, because they intercept all new window requests and rely on the embedder's javascript to handle them (e.g. by forwarding to chrome.tabs.create API).  Without such forwarding the creation of a new window is blocked with an error message saying: "<webview>: A new window was blocked".  I am not sure if the forwarding can result in the new window being handled by WebContentsImpl::CreateNewWindow.

I am not sure if other guest views might still need the GuestViewBase::AddNewContents override.

This issue is a follow-up for  issue 796080 .