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
 // to. Connections to applications not explicitly specified here as a key are
 // rejected. Connections to services not specified in an application's allowed
 // interfaces value are not made.
 // A "*" value as the only key in an otherwise empty map means the application
 // may connect to any other application.
 // A "*" value as the only string in an otherwise empty array of interface names
 // means the application may connect to any service in that application.
 // An empty interface name array means the application may not connect to any
 // services exposed by the application it is connecting to.
 struct CapabilityFilter {
   map<string, array<string>> filter;
 };
 
 // An interface through which a Mojo application may communicate with the Mojo
 // system and request connections to other applications.
 interface Shell {
+  // Used to indicate the app was not launched by a content handler.
+  const uint32 kInvalidContentHandlerID = 0;
+
   // Establishes a connection with another application ("target application")
   // (located at |request->url|) through which the calling application and the
   // target application may request services from one another.
   // |application_url| is a URLRequest in case this is called for an HTTP
   // navigation, in which case HTTP specific information like POST data,
   // referrer header etc... needed.
   //
   // If the calling application would like to request services from the target
   // application, it should pass a valid interface request in the |services|
   // parameter (i.e. one containing a valid message pipe endpoint). If the
@@ skipping 12 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 kInvalidContentHandlerID.
+  // 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();
 };