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() : 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;
+
+  focused_windows_.insert(window);
+  if (window)
+    observer_manager_.Add(window);
+
+  for (aura::client::FocusChangeObserver& observer : focus_observers_)
+    observer.OnWindowFocused(window, NULL);
+  aura::client::FocusChangeObserver* observer =
+      aura::client::GetFocusChangeObserver(window);
+  if (observer)
+    observer->OnWindowFocused(window, NULL);
+}
+
+void HeadlessFocusClient::ResetFocusWithinActiveWindow(aura::Window* window) {
+  for (auto focused_window : focused_windows_) {
+    if (focused_window->Contains(window)) {
+      FocusWindow(window);
+      break;
+    }
+  }
+}
+
+aura::Window* HeadlessFocusClient::GetFocusedWindow() {

[irisu, 2017/02/24 04:48:31]

I'm not sure what we'd want to return here. Just returning one of the focused
windows for now. :)

[Eric Seckler, 2017/02/27 08:39:38]

Hmm, I see. Looks like aura doesn't really support multiple focused windows -
GetFocusedWindow() is used for a variety of things, via others
aura::Window::HasFocus(), even RWHVAura::HasFocus() relies on it :(

Let's just track a single window for focus then. To make focus tab-independent,
we'll have to move to multiple WindowTreeHosts afterall, I think. Sorry for
pointing you in the wrong direction!

+  if (focused_windows_.empty())
+    return NULL;
+  return *focused_windows_.begin();
+}
+
+void HeadlessFocusClient::OnWindowDestroying(aura::Window* window) {
+  observer_manager_.Remove(window);
+  focused_windows_.erase(window);
+}
+
+}  // namespace headless