Enable the mojo-based serial API in the renderer behind a flag.

extensions/browser/service_registration_manager.cc

Index: extensions/browser/service_registration_manager.cc
diff --git a/extensions/browser/service_registration_manager.cc b/extensions/browser/service_registration_manager.cc
index 00129a11206a8d9db603062c37cb161854e768d1..992f2627a105b32a04177064e7fc395b80f0c3db 100644
--- a/extensions/browser/service_registration_manager.cc
+++ b/extensions/browser/service_registration_manager.cc
@@ -23,6 +23,8 @@ namespace {
 base::LazyInstance<ServiceRegistrationManager> g_lazy_instance =
     LAZY_INSTANCE_INITIALIZER;
 
+ServiceRegistrationManager* g_test_instance = nullptr;
+
 }  // namespace
 
 ServiceRegistrationManager::ServiceRegistrationManager() {
@@ -44,6 +46,8 @@ ServiceRegistrationManager::~ServiceRegistrationManager() {
 }
 
 ServiceRegistrationManager* ServiceRegistrationManager::GetSharedInstance() {
+  if (g_test_instance)
+    return g_test_instance;
   return g_lazy_instance.Pointer();
 }
 
@@ -72,9 +76,27 @@ void ServiceRegistrationManager::AddServicesToRenderFrame(
     if (ExtensionAPI::GetSharedInstance()
             ->IsAvailable(factory.first, extension, context_type, extension_url)
             .is_available()) {
-      factory.second->Register(render_frame_host->GetServiceRegistry());
+      AddServiceToServiceRegistry(render_frame_host->GetServiceRegistry(),
+                                  factory.second.get());
     }
   }
 }
 
+void ServiceRegistrationManager::AddServiceToServiceRegistry(
+    content::ServiceRegistry* service_registry,
+    internal::ServiceFactoryBase* factory) {
+  factory->Register(service_registry);
+}
+
+// static
+void ServiceRegistrationManager::SetServiceRegistrationManagerForTest(
+    ServiceRegistrationManager* service_registration_manager) {
+  g_test_instance = service_registration_manager;
+}
+
+// static
+void ServiceRegistrationManager::ClearServiceRegistrationManagerForTest() {

[raymes, 2014/10/24 00:09:30]

nit: this isn't really needed right, you could just call
SetServiceRegistrationManagerForTest(NULL)

[Sam McNally, 2014/10/24 03:55:56]

Done.

+  g_test_instance = nullptr;
+}
+
 }  // namespace extensions