[Athena, Cleanup] rename WidnowManager::GetInstance -> ::Get

athena/content/app_activity.cc

Index: athena/content/app_activity.cc
diff --git a/athena/content/app_activity.cc b/athena/content/app_activity.cc
index da5f929847a701d836818d0eb14e652632e23148..4315df3d8c39de83d45c63ccef96ab0058a1fea8 100644
--- a/athena/content/app_activity.cc
+++ b/athena/content/app_activity.cc
@@ -103,7 +103,7 @@ void AppActivity::Init() {
     // Note: At this time the |AppActivity| did not get registered to the
     // |ResourceManager| - so we can move it around if needed.
     WindowListProvider* window_list_provider =
-        WindowManager::GetInstance()->GetWindowListProvider();
+        WindowManager::Get()->GetWindowListProvider();
     window_list_provider->StackWindowFrontOf(app_proxy->GetWindow(),
                                              GetWindow());
     Activity::Delete(app_proxy);