WIP: Eliminate event.target() usage from TrayEventFilter

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
index 413ea71bb58bd019f77ac92646754bfb1207b0a6..67becb93e4bcc23e457d5e79ecbb03c7276087a5 100644
--- a/ash/pointer_watcher_delegate_aura.cc
+++ b/ash/pointer_watcher_delegate_aura.cc
@@ -11,6 +11,7 @@
 #include "ui/events/event_constants.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/views/pointer_watcher.h"
+#include "ui/views/widget/widget.h"
 
 namespace ash {
 
@@ -35,13 +36,21 @@ void PointerWatcherDelegateAura::RemovePointerWatcher(
 void PointerWatcherDelegateAura::OnMouseEvent(ui::MouseEvent* event) {
   if (event->type() == ui::ET_MOUSE_PRESSED)
     FOR_EACH_OBSERVER(views::PointerWatcher, pointer_watchers_,
-                      OnMousePressed(*event, GetLocationInScreen(*event)));
+                      OnMousePressed(*event, GetLocationInScreen(*event),
+                                     GetTargetWidget(*event)));
 }
 
 void PointerWatcherDelegateAura::OnTouchEvent(ui::TouchEvent* event) {
   if (event->type() == ui::ET_TOUCH_PRESSED)
     FOR_EACH_OBSERVER(views::PointerWatcher, pointer_watchers_,
-                      OnTouchPressed(*event, GetLocationInScreen(*event)));
+                      OnTouchPressed(*event, GetLocationInScreen(*event),
+                                     GetTargetWidget(*event)));
+}
+
+views::Widget* PointerWatcherDelegateAura::GetTargetWidget(
+    const ui::LocatedEvent& event) const {
+  aura::Window* window = static_cast<aura::Window*>(event.target());
+  return views::Widget::GetTopLevelWidgetForNativeView(window);
 }
 
 gfx::Point PointerWatcherDelegateAura::GetLocationInScreen(