mash: Close system tray bubble on click outside its bounds, part 1

ui/views/mus/platform_window_mus.cc

Index: ui/views/mus/platform_window_mus.cc
diff --git a/ui/views/mus/platform_window_mus.cc b/ui/views/mus/platform_window_mus.cc
index d42a9a779089a7a6ac0ee413b97206cec6d48b07..e536858771c8ae3129b79b4538c1595dea9608f2 100644
--- a/ui/views/mus/platform_window_mus.cc
+++ b/ui/views/mus/platform_window_mus.cc
@@ -227,6 +227,9 @@ void PlatformWindowMus::OnWindowInputEvent(
   // It's possible dispatching the event will spin a nested message loop. Ack
   // the callback now, otherwise we appear unresponsive for the life of the
   // nested message loop.
+  // TODO(jamescook): Only ack the event as handled if a nested message loop
+  // actually starts, perhaps through an observer on MessageLoop. Otherwise
+  // ack the event with the actual handled state below DispatchEvent().
   (*ack_callback)->Run(true);
   ack_callback->reset();
   // TODO(moshayedi): Avoid cloning after updating PlatformWindowDelegate to