mus: Add PointerWatcher for passively observing mouse and touch events

ash/pointer_watcher_delegate_aura.cc

+// Copyright 2016 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 "ash/pointer_watcher_delegate_aura.h"
+
+#include "ash/shell.h"
+#include "ui/events/event.h"
+#include "ui/events/event_constants.h"
+#include "ui/views/pointer_watcher.h"
+
+namespace ash {
+
+PointerWatcherDelegateAura::PointerWatcherDelegateAura() {}
+
+PointerWatcherDelegateAura::~PointerWatcherDelegateAura() {}
+
+void PointerWatcherDelegateAura::AddPointerWatcher(
+    views::PointerWatcher* watcher) {
+  bool had_observers = pointer_watchers_.might_have_observers();
+  pointer_watchers_.AddObserver(watcher);
+  if (!had_observers) {
+    Shell::GetInstance()->AddPreTargetHandler(this);
+  }
+}
+
+void PointerWatcherDelegateAura::RemovePointerWatcher(
+    views::PointerWatcher* watcher) {
+  pointer_watchers_.RemoveObserver(watcher);
+  if (!pointer_watchers_.might_have_observers()) {

[sky, 2016/04/26 21:44:45]

One question here. This is named might for a reason. At certain times this can
return true even if there are no observers. Do you really need to use it?

[James Cook, 2016/04/26 23:19:05]

Discussed offline. I converted this one to always install itself via
AddPreTargetHandler() and the one in WindowManagerConnection to use
base::ObserverList<>::Iterator to check if the observer list is empty.

+    // We removed the last PointerWatcher, so no need to monitor events.
+    Shell::GetInstance()->RemovePreTargetHandler(this);
+  }
+}
+
+void PointerWatcherDelegateAura::OnMouseEvent(ui::MouseEvent* event) {
+  if (event->type() == ui::ET_MOUSE_PRESSED)
+    FOR_EACH_OBSERVER(views::PointerWatcher, pointer_watchers_,
+                      OnMousePressed(*event));
+}
+
+void PointerWatcherDelegateAura::OnTouchEvent(ui::TouchEvent* event) {
+  if (event->type() == ui::ET_TOUCH_PRESSED)
+    FOR_EACH_OBSERVER(views::PointerWatcher, pointer_watchers_,
+                      OnTouchPressed(*event));
+}
+
+}  // namespace ash