Mojo C++ bindings: switch mash/init mojom target to use STL types.

mash/init/init.h

Index: mash/init/init.h
diff --git a/mash/init/init.h b/mash/init/init.h
index 4ee523f1b54a4cd60c6be64a525868506c0c6834..e1987a9b6aceee26d8a723cd30d59915be7b568b 100644
--- a/mash/init/init.h
+++ b/mash/init/init.h
@@ -42,9 +42,9 @@ class Init : public service_manager::Service,
               mojom::InitRequest request) override;
 
   // mojom::Init:
-  void StartService(const mojo::String& name,
-                    const mojo::String& user_id) override;
-  void StopServicesForUser(const mojo::String& user_id) override;
+  void StartService(const std::string& name,
+                    const std::string& user_id) override;
+  void StopServicesForUser(const std::string& user_id) override;
 
   void UserServiceQuit(const std::string& user_id);