First cut at "content handling" support in Mojo.

mojo/shell/dbus_service_loader_linux.cc

Index: mojo/shell/dbus_service_loader_linux.cc
diff --git a/mojo/shell/dbus_service_loader_linux.cc b/mojo/shell/dbus_service_loader_linux.cc
index af4e0d4422ed058d9ef7c52552218c0e01d46b87..934637e474c49e71685b91574cc43f073c74e9e4 100644
--- a/mojo/shell/dbus_service_loader_linux.cc
+++ b/mojo/shell/dbus_service_loader_linux.cc
@@ -150,9 +150,15 @@ DBusServiceLoader::~DBusServiceLoader() {
   DCHECK(url_to_load_context_.empty());
 }
 
-void DBusServiceLoader::LoadService(ServiceManager* manager,
-                                    const GURL& url,
-                                    ScopedMessagePipeHandle shell_handle) {
+void DBusServiceLoader::Load(ServiceManager* manager,
+                             const GURL& url,
+                             scoped_refptr<LoadCallbacks> callbacks) {
+  // TODO(aa): This could be delayed until later, when we know that loading is
+  // going to succeed.
+  ScopedMessagePipeHandle shell_handle = callbacks->RegisterApplication();
+  if (!shell_handle.is_valid())
+    return;
+
   DCHECK(url.SchemeIs("dbus"));
   DCHECK(url_to_load_context_.find(url) == url_to_load_context_.end());
   url_to_load_context_[url] =