Add HeadlessFocusClient to fix document.hasFocus() issues.

headless/lib/browser/headless_focus_client.cc

+// 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.
+
+#include "headless/lib/browser/headless_focus_client.h"
+
+#include "ui/aura/client/focus_change_observer.h"
+#include "ui/aura/window.h"
+
+namespace headless {
+
+HeadlessFocusClient::HeadlessFocusClient()
+    : focused_window_(NULL), observer_manager_(this) {}
+
+HeadlessFocusClient::~HeadlessFocusClient() {}
+
+void HeadlessFocusClient::AddObserver(
+    aura::client::FocusChangeObserver* observer) {
+  focus_observers_.AddObserver(observer);
+}
+
+void HeadlessFocusClient::RemoveObserver(
+    aura::client::FocusChangeObserver* observer) {
+  focus_observers_.RemoveObserver(observer);
+}
+
+void HeadlessFocusClient::FocusWindow(aura::Window* window) {
+  if (window && !window->CanFocus())
+    return;
+
+  if (focused_window_)
+    observer_manager_.Remove(focused_window_);
+  aura::Window* old_focused_window = focused_window_;
+  focused_window_ = window;
+  if (focused_window_)
+    observer_manager_.Add(focused_window_);
+
+  for (aura::client::FocusChangeObserver& observer : focus_observers_)
+    observer.OnWindowFocused(focused_window_, old_focused_window);
+  aura::client::FocusChangeObserver* observer =
+      aura::client::GetFocusChangeObserver(old_focused_window);
+  if (observer)
+    observer->OnWindowFocused(focused_window_, old_focused_window);
+  observer = aura::client::GetFocusChangeObserver(focused_window_);
+  if (observer)
+    observer->OnWindowFocused(focused_window_, old_focused_window);
+}
+
+void HeadlessFocusClient::ResetFocusWithinActiveWindow(aura::Window* window) {
+  if (!window->Contains(focused_window_))
+    FocusWindow(window);
+}
+
+aura::Window* HeadlessFocusClient::GetFocusedWindow() {
+  return focused_window_;
+}
+
+void HeadlessFocusClient::OnWindowDestroying(aura::Window* window) {
+  DCHECK_EQ(window, focused_window_);
+  FocusWindow(NULL);
+}
+
+}  // namespace headless