mus: Add PointerWatcher for passively observing mouse and touch events

ash/pointer_watcher_delegate_aura.cc

Index: ash/pointer_watcher_delegate_aura.cc
diff --git a/ash/pointer_watcher_delegate_aura.cc b/ash/pointer_watcher_delegate_aura.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c00ff1c0263904ebb6b54ab16378b22010c1581b
--- /dev/null
+++ b/ash/pointer_watcher_delegate_aura.cc
@@ -0,0 +1,48 @@
+// 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() {}

[sky, 2016/04/26 16:55:48]

Remove pretargethandler if have observers?

[James Cook, 2016/04/26 17:42:45]

I went with ObserverList check_empty. I think that makes it more likely that a
developer will catch that he's leaking observers on shutdown (which I find
painful to debug).

+
+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()) {
+    // 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