Adds a way to determine id of content handler that created app

mojo/application/public/interfaces/shell.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/application/public/interfaces/service_provider.mojom";
 import "network/public/interfaces/url_loader.mojom";
 
 // Specifies a whitelist of applications and services an application can connect
@@ skipping 38 matching lines @@
   // If the |application_url| does not contain a domain, but is of the form
   // "mojo:{service}", it is up to the Mojo shell to select an appropriate
   // application for the service. Currently, the shell does this based on the
   // value of its --origin flag.
   //
   // |filter| is a whitelist of application URLs and services that the target
   // application is permitted to connect to. See documentation for
   // CapabilityFilter above. Note also that this parameter may be NULL, which
   // has the same meaning as allowing the target application to connect to
   // any application and service.
+  //
+  // If the connection to |application_url| involves a content handler, then
+  // |content_handler_id| is the id of the deepest content handler used to
+  // establish the connection to |application_url|. If no content handler is
+  // used |content_handler_id| is 0.

[Ben Goodger (Google), 2015/08/31 17:41:07]

since this looks a little arbitrary... add:

TODO(beng): determine if we need to expose the target application id also.

   ConnectToApplication(URLRequest application_url,
                        ServiceProvider&? services,
                        ServiceProvider? exposed_services,
-                       CapabilityFilter? filter);
+                       CapabilityFilter? filter) => (uint32 content_handler_id);
 
   // When there are no more instantiated services in an application, it should
   // start its shutdown process by calling this method. Additionally, it should
   // keep track of any new service requests that come in. The shell will then
   // call Application::OnQuitRequested and start queueing new service requests.
   // If the application didn't get any new service requests in the meantime, it
   // should call the callback with a true value. Otherwise it should call it
   // with false.
   QuitApplication();
 };