First cut at "content handling" support in Mojo.

mojo/shell/view_manager_loader.cc

Index: mojo/shell/view_manager_loader.cc
diff --git a/mojo/shell/view_manager_loader.cc b/mojo/shell/view_manager_loader.cc
index bbcca5ae64042635cb2471baf47f411b534f8f6f..870344ef79a63aa37ce6b3223b6be7b30c657a4a 100644
--- a/mojo/shell/view_manager_loader.cc
+++ b/mojo/shell/view_manager_loader.cc
@@ -23,7 +23,12 @@ ViewManagerLoader::~ViewManagerLoader() {
 void ViewManagerLoader::LoadService(
     ServiceManager* manager,
     const GURL& url,
-    ScopedMessagePipeHandle shell_handle) {
+    scoped_refptr<LoadServiceCallbacks> callbacks) {
+  ScopedMessagePipeHandle shell_handle = callbacks->RegisterApplication();
+  if (!shell_handle.is_valid()) {
+    return;
+  }
+
   // TODO(sky): this needs some sort of authentication as well as making sure
   // we only ever have one active at a time.
   scoped_ptr<ApplicationImpl> app(