mash: Remove ash::ShelfGestureHandler and ui::ET_GESTURE_WIN8_EDGE_SWIPE

ash/shelf/shelf_view.cc

Index: ash/shelf/shelf_view.cc
diff --git a/ash/shelf/shelf_view.cc b/ash/shelf/shelf_view.cc
index c465a904f0427d76787b8f42eff88b0e1f04c5f2..44cd83d6d66f76e5f1e028f9803e844a215506fc 100644
--- a/ash/shelf/shelf_view.cc
+++ b/ash/shelf/shelf_view.cc
@@ -1543,10 +1543,7 @@ void ShelfView::ViewHierarchyChanged(
 }
 
 void ShelfView::OnGestureEvent(ui::GestureEvent* event) {
-  aura::Window* target_window = static_cast<views::View*>(event->target())
-                                    ->GetWidget()
-                                    ->GetNativeWindow();
-  if (gesture_handler_.ProcessGestureEvent(*event, target_window))
+  if (wm_shelf_->ProcessGestureEvent(*event))
     event->StopPropagation();
 }