aura-mus: Implement Deactivate().

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 13509d8465987ee47d7acac229e0c3e1a037663f..b27154446694906453cb95f1541eb088d1fb6e43 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -504,5 +504,13 @@ void WindowManager::OnWmSetClientArea(
   non_client_frame_controller->SetClientArea(insets, additional_client_areas);
 }
 
+bool WindowManager::IsWindowActive(aura::Window* window) {
+  return activation_client()->GetActiveWindow() == window;
+}
+
+void WindowManager::OnWmDeactivateWindow(aura::Window* window) {
+  activation_client()->DeactivateWindow(window);
+}
+
 }  // namespace mus
 }  // namespace ash