Converts test_wm to use aura

ui/aura/mus/focus_synchronizer.cc

Index: ui/aura/mus/focus_synchronizer.cc
diff --git a/ui/aura/mus/focus_synchronizer.cc b/ui/aura/mus/focus_synchronizer.cc
index 8f69615ed114e661e44532fe83df35feb6538795..b211315fc9ca0c97d991b01993559d1fe0cd4d51 100644
--- a/ui/aura/mus/focus_synchronizer.cc
+++ b/ui/aura/mus/focus_synchronizer.cc
@@ -33,11 +33,13 @@ void FocusSynchronizer::SetFocusFromServer(WindowMus* window) {
   base::AutoReset<bool> focus_reset(&setting_focus_, true);
   base::AutoReset<WindowMus*> window_setting_focus_to_reset(
       &window_setting_focus_to_, window);
-  Env* env = aura::Env::GetInstance();
+  Env* env = Env::GetInstance();
   if (window) {
     Window* root = window->GetWindow()->GetRootWindow();
+    // The client should provide a focus client for all roots.
+    DCHECK(client::GetFocusClient(root));
     if (env->active_focus_client_root() != root)
-      env->SetActiveFocusClient(aura::client::GetFocusClient(root), root);
+      env->SetActiveFocusClient(client::GetFocusClient(root), root);
     window->GetWindow()->Focus();
   } else if (env->active_focus_client()) {
     env->active_focus_client()->FocusWindow(nullptr);