[Chromecast] Add support for z-order and window focus.

chromecast/graphics/cast_focus_client_aura.h

Index: chromecast/graphics/cast_focus_client_aura.h
diff --git a/chromecast/graphics/cast_focus_client_aura.h b/chromecast/graphics/cast_focus_client_aura.h
new file mode 100644
index 0000000000000000000000000000000000000000..c628800f902853aa722b9d4abf0b3e27fec03ce1
--- /dev/null
+++ b/chromecast/graphics/cast_focus_client_aura.h
@@ -0,0 +1,63 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMECAST_GRAPHICS_CAST_FOCUS_CLIENT_AURA_H_
+#define CHROMECAST_GRAPHICS_CAST_FOCUS_CLIENT_AURA_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "ui/aura/client/focus_change_observer.h"
+#include "ui/aura/client/focus_client.h"
+#include "ui/aura/window_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace chromecast {
+
+class CastFocusClientAura : public aura::WindowObserver,
+                            public aura::client::FocusClient {
+ public:
+  CastFocusClientAura();
+  ~CastFocusClientAura() override;
+
+  // aura::client::FocusClient implementation:
+  void AddObserver(aura::client::FocusChangeObserver* observer) override;
+  void RemoveObserver(aura::client::FocusChangeObserver* observer) override;
+  void FocusWindow(aura::Window* window) override;
+  void ResetFocusWithinActiveWindow(aura::Window* window) override;
+  aura::Window* GetFocusedWindow() override;
+
+ private:
+  // aura::WindowObserver implementation:
+  void OnWindowVisibilityChanged(aura::Window* window, bool visible) override;
+  void OnWindowDestroying(aura::Window* window) override;
+  void OnWindowHierarchyChanging(const HierarchyChangeParams& params) override;
+
+  // Change the focused window and notify focus observers.
+  void UpdateWindowFocus();
+  // Get the window that should be focused.
+  aura::Window* GetWindowToFocus();
+  // Get the top-most window in a window's hierarchy.
+  aura::Window* GetTopLevelWindow(aura::Window* window);
+
+  base::ObserverList<aura::client::FocusChangeObserver> focus_observers_;
+
+  // Track the currently focused window, which isn't necessarily a top-level
+  // window.
+  aura::Window* focused_window_;
+  // Track the windows that we've focused in the past, so that we can restore
+  // focus to them.  We assume that this is a small list so that we can perform
+  // linear ops on it.
+  std::vector<aura::Window*> focusable_windows_;
+
+  DISALLOW_COPY_AND_ASSIGN(CastFocusClientAura);
+};
+
+}  // namespace chromecast
+
+#endif  // CHROMECAST_GRAPHICS_CAST_FOCUS_CLIENT_AURA_H_