Context menu on views must show on mouse down for non-WIN.

ui/views/widget/root_view.cc

Index: ui/views/widget/root_view.cc
diff --git a/ui/views/widget/root_view.cc b/ui/views/widget/root_view.cc
index 1092f2dbd6b95e285e08be18136387146af17342..dfc9d8a3230e614efec588caa28a7687861babda 100644
--- a/ui/views/widget/root_view.cc
+++ b/ui/views/widget/root_view.cc
@@ -433,7 +433,12 @@ bool RootView::OnMousePressed(const ui::MouseEvent& event) {
       mouse_pressed_event.set_flags(event.flags() & ~ui::EF_IS_DOUBLE_CLICK);
 
     drag_info_.Reset();
-    DispatchEventToTarget(mouse_pressed_handler_, &mouse_pressed_event);
+    {
+      WidgetDeletionObserver widget_deletion_observer(widget_);
+      DispatchEventToTarget(mouse_pressed_handler_, &mouse_pressed_event);
+      if (!widget_deletion_observer.IsWidgetAlive())
+        return mouse_pressed_event.handled();
+    }
 
     // The view could have removed itself from the tree when handling
     // OnMousePressed().  In this case, the removal notification will have