mojo: kill app_thread before unloading main app library and add tests

mojo/service_manager/service_manager.cc

Index: mojo/service_manager/service_manager.cc
diff --git a/mojo/service_manager/service_manager.cc b/mojo/service_manager/service_manager.cc
index 92d336ca5b788694aa93a17f1d6f005b9580491b..0f13cfde6b375231d69db0fdd336a8d5a1f18788 100644
--- a/mojo/service_manager/service_manager.cc
+++ b/mojo/service_manager/service_manager.cc
@@ -94,11 +94,15 @@ ServiceManager::ServiceManager() : interceptor_(NULL) {
 }
 
 ServiceManager::~ServiceManager() {
-  STLDeleteValues(&url_to_shell_impl_);
+  TerminateShellConnections();
   STLDeleteValues(&url_to_loader_);
   STLDeleteValues(&scheme_to_loader_);
 }
 
+void ServiceManager::TerminateShellConnections() {
+  STLDeleteValues(&url_to_shell_impl_);
+}
+
 // static
 ServiceManager* ServiceManager::GetInstance() {
   static base::LazyInstance<ServiceManager> instance =
@@ -157,7 +161,6 @@ ServiceLoader* ServiceManager::GetLoaderForURL(const GURL& url) {
       scheme_to_loader_.find(url.scheme());
   if (scheme_it != scheme_to_loader_.end())
     return scheme_it->second;
-  DCHECK(default_loader_);
   return default_loader_.get();
 }