chromeos: fix focus for mushrome

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 1e1e408ad5b9362f1270bf91b3ee1774a8e20fc9..cc24e7e7adf47b3245e79168f3e97a32e3da2f41 100644
--- a/ui/aura/mus/focus_synchronizer.cc
+++ b/ui/aura/mus/focus_synchronizer.cc
@@ -42,7 +42,9 @@ void FocusSynchronizer::SetFocusFromServer(WindowMus* window) {
     Window* root = window->GetWindow()->GetRootWindow();
     // The client should provide a focus client for all roots.
     DCHECK(client::GetFocusClient(root));
-    if (active_focus_client_root_ != root)
+    if (is_singleton_focus_client_)
+      DCHECK_EQ(active_focus_client_, client::GetFocusClient(root));
+    else if (active_focus_client_root_ != root)
       SetActiveFocusClient(client::GetFocusClient(root), root);
     window->GetWindow()->Focus();
   } else if (active_focus_client_) {
@@ -54,19 +56,31 @@ void FocusSynchronizer::OnFocusedWindowDestroyed() {
   focused_window_ = nullptr;
 }
 
+void FocusSynchronizer::SetSingletonFocusClient(
+    client::FocusClient* focus_client) {
+  SetActiveFocusClient(focus_client, nullptr);
+  if (focus_client)
+    is_singleton_focus_client_ = true;
+}
+
 void FocusSynchronizer::SetActiveFocusClient(client::FocusClient* focus_client,
                                              Window* focus_client_root) {
-  if (focus_client_root == active_focus_client_root_) {
-    DCHECK_EQ(focus_client, active_focus_client_);
+  if (focus_client == active_focus_client_ &&
+      focus_client_root == active_focus_client_root_) {
     return;
   }
 
+  is_singleton_focus_client_ = false;
+
   if (active_focus_client_root_)
     active_focus_client_root_->RemoveObserver(this);
   active_focus_client_root_ = focus_client_root;
   if (active_focus_client_root_)
     active_focus_client_root_->AddObserver(this);
 
+  if (focus_client == active_focus_client_)
+    return;
+
   OnActiveFocusClientChanged(focus_client, focus_client_root);
   for (FocusSynchronizerObserver& observer : observers_)
     observer.OnActiveFocusClientChanged(focus_client, focus_client_root);
@@ -118,12 +132,14 @@ void FocusSynchronizer::OnWindowFocused(Window* gained_focus,
 }
 
 void FocusSynchronizer::OnWindowDestroying(Window* window) {
+  DCHECK(!is_singleton_focus_client_);
   SetActiveFocusClient(nullptr, nullptr);
 }
 
 void FocusSynchronizer::OnWindowPropertyChanged(Window* window,
                                                 const void* key,
                                                 intptr_t old) {
+  DCHECK(!is_singleton_focus_client_);
   if (key != client::kFocusClientKey)
     return;