Pass the final URL an app was loaded from to the app in Initialize().

mojo/public/interfaces/application/application.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo;
 
 import "mojo/public/interfaces/application/service_provider.mojom";
 import "mojo/public/interfaces/application/shell.mojom";
 
 // This is the primary interface implemented by every Mojo application. It
 // allows the application to receive its startup arguments from the shell, and
 // to be notified of events that occur during its execution.
 interface Application {
   // Initializes the application with the specified arguments. This method is
   // guaranteed to be called before any other method is called, and will only be
-  // called once.
-  Initialize(Shell shell, array<string>? args);
+  // called once. The |url| parameter is the final url the application was found
+  // at, after all redirects and resolutions.
+  Initialize(Shell shell, array<string>? args, string url);
 
   // Called when another application (identified by |requestor_url|) attempts to
   // open a connection to this application.
   //
   // If the other application wants to request services from this application,
   // it will have passed a valid interface request through the |services|
   // parameter (i.e. one containing a valid message pipe endpoint). This
   // application may then bind an implementation of |ServiceProvider| to that
   // request in order to make services available to the other application.
   //
   // If the other application wants to offer services to this application, it
   // will have passed a bound interface through the |exposed_services|
   // parameter. This application may then request services through that
   // interface.
   //
   // It is possible that both parameters will be valid/bound if the other
   // application wants to both request services from and offer services to this
   // application.
   //
   // This application is free to ignore the |services| or |exposed_services|
   // parameters if it does not wish to offer or request services.
   AcceptConnection(string requestor_url,
                    ServiceProvider&? services,
                    ServiceProvider? exposed_services);
 
   // Called to request the application shut itself down gracefully.
   RequestQuit();
 };