REVIEW: Delete WidgetDelegate before widget is destroyed.

Ideally widget delegates must outlive their widget, but since
we manage the lifetime of native widget, allow the delegate to
be destroyed when widget is destroyed.
https://chromium-review.googlesource.com/c/chromium/src/+/977244

atom/browser/native_window.cc

@@ -60,7 +60,10 @@ NativeWindow::NativeWindow(const mate::Dictionary& options,
 
 NativeWindow::~NativeWindow() {
   // It's possible that the windows gets destroyed before it's closed, in that
-  // case we need to ensure the OnWindowClosed message is still notified.
+  // case we need to ensure the Widget delegate gets destroyed and
+  // OnWindowClosed message is still notified.
+  if (widget_->widget_delegate())
+    widget_->OnNativeWidgetDestroyed();
   NotifyWindowClosed();
 }