Add HeadlessFocusClient to fix document.hasFocus() issues.

headless/lib/browser/headless_focus_client.h

+// 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 HEADLESS_LIB_BROWSER_HEADLESS_FOCUS_CLIENT_H_
+#define HEADLESS_LIB_BROWSER_HEADLESS_FOCUS_CLIENT_H_
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "base/scoped_observer.h"
+#include "ui/aura/client/focus_client.h"
+#include "ui/aura/window_observer.h"
+
+namespace headless {
+
+class HeadlessFocusClient : public aura::client::FocusClient,
+                            public aura::WindowObserver {
+ public:
+  HeadlessFocusClient();
+  ~HeadlessFocusClient() override;
+
+ private:
+  // Overridden from aura::client::FocusClient:
+  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;
+
+  // Overridden from aura::WindowObserver:
+  void OnWindowDestroying(aura::Window* window) override;
+
+  aura::Window* focused_window_;
+  ScopedObserver<aura::Window, aura::WindowObserver> observer_manager_;
+  base::ObserverList<aura::client::FocusChangeObserver> focus_observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(HeadlessFocusClient);
+};
+
+}  // namespace headless
+
+#endif  // HEADLESS_LIB_BROWSER_HEADLESS_FOCUS_CLIENT_H_