Improves focus/activation for aura-mus and DesktopNativeWidgetAura

ui/aura/env.h

Index: ui/aura/env.h
diff --git a/ui/aura/env.h b/ui/aura/env.h
index d557a1f50f54d8f82d6276feaa940d017d1fb135..acd289b4c580e829932698ef9f9716ac5129edaf 100644
--- a/ui/aura/env.h
+++ b/ui/aura/env.h
@@ -22,6 +22,10 @@ class PlatformEventSource;
 }
 namespace aura {
 
+namespace client {
+class FocusClient;
+}
+
 namespace test {
 class EnvTestHelper;
 }
@@ -74,7 +78,17 @@ class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
   }
   ui::ContextFactory* context_factory() { return context_factory_; }
 
+  // Sets the active FocusClient and the window the FocusClient is associated
+  // with. |window| is not necessarily the window that actually has focus.
+  // |window| may be null, which indicates all windows share a FocusClient.
+  void SetActiveFocusClient(client::FocusClient* focus_client,
+                            Window* focus_client_root);
+  client::FocusClient* active_focus_client() { return active_focus_client_; }
+  Window* active_focus_client_root() { return active_focus_client_root_; }
+
  private:
+  class ActiveFocusClientWindowObserver;
+
   friend class test::EnvTestHelper;
   friend class Window;
   friend class WindowTreeHost;
@@ -92,6 +106,8 @@ class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
   // Invoked by WindowTreeHost when it is activated. Notifies observers.
   void NotifyHostActivated(WindowTreeHost* host);
 
+  void OnActiveFocusClientWindowDestroying();
+
   // Overridden from ui::EventTarget:
   bool CanAcceptEvent(const ui::Event& event) override;
   ui::EventTarget* GetParentTarget() override;
@@ -112,6 +128,11 @@ class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
 
   ui::ContextFactory* context_factory_;
 
+  Window* active_focus_client_root_ = nullptr;
+  client::FocusClient* active_focus_client_ = nullptr;
+  std::unique_ptr<ActiveFocusClientWindowObserver>
+      active_focus_client_window_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(Env);
 };