First cut at "content handling" support in Mojo.

mojo/service_manager/background_service_loader.cc

Index: mojo/service_manager/background_service_loader.cc
diff --git a/mojo/service_manager/background_service_loader.cc b/mojo/service_manager/background_service_loader.cc
index 8c60a2cc00696df313e989933dcf63d6875d480f..dc6d9b6cdee8c60debb137f1b7b661e15100ad83 100644
--- a/mojo/service_manager/background_service_loader.cc
+++ b/mojo/service_manager/background_service_loader.cc
@@ -17,7 +17,9 @@ class BackgroundServiceLoader::BackgroundLoader {
   void LoadService(ServiceManager* manager,
                    const GURL& url,
                    ScopedMessagePipeHandle shell_handle) {
-    loader_->LoadService(manager, url, shell_handle.Pass());
+    scoped_refptr<LoadServiceCallbacks> callbacks(
+        new ServiceLoader::SimpleLoadServiceCallbacks(shell_handle.Pass()));
+    loader_->LoadService(manager, url, callbacks);
   }
 
   void OnServiceError(ServiceManager* manager, const GURL& url) {
@@ -54,8 +56,14 @@ BackgroundServiceLoader::~BackgroundServiceLoader() {
 void BackgroundServiceLoader::LoadService(
     ServiceManager* manager,
     const GURL& url,
-    ScopedMessagePipeHandle shell_handle) {
+    scoped_refptr<LoadServiceCallbacks> callbacks) {
   const int kDefaultStackSize = 0;
+
+  ScopedMessagePipeHandle shell_handle = callbacks->RegisterApplication();
+  if (!shell_handle.is_valid()) {
+    return;
+  }
+
   if (!thread_.IsRunning()) {
     thread_.StartWithOptions(
         base::Thread::Options(message_loop_type_, kDefaultStackSize));
@@ -64,8 +72,7 @@ void BackgroundServiceLoader::LoadService(
       FROM_HERE,
       base::Bind(&BackgroundServiceLoader::LoadServiceOnBackgroundThread,
                  base::Unretained(this), manager, url,
-                 base::Owned(
-                    new ScopedMessagePipeHandle(shell_handle.Pass()))));
+                 base::Passed(&shell_handle)));
 }
 
 void BackgroundServiceLoader::OnServiceError(ServiceManager* manager,
@@ -81,11 +88,11 @@ void BackgroundServiceLoader::OnServiceError(ServiceManager* manager,
 void BackgroundServiceLoader::LoadServiceOnBackgroundThread(
     ServiceManager* manager,
     const GURL& url,
-    ScopedMessagePipeHandle* shell_handle) {
+    ScopedMessagePipeHandle shell_handle) {
   if (!background_loader_)
     background_loader_ = new BackgroundLoader(loader_.get());
   background_loader_->LoadService(
-      manager, url, shell_handle->Pass());
+      manager, url, shell_handle.Pass());
 }
 
 void BackgroundServiceLoader::OnServiceErrorOnBackgroundThread(