views: Add comment to Combobox's native wrapper about its lifetime.

views/controls/combobox/combobox.cc

Index: views/controls/combobox/combobox.cc
diff --git a/views/controls/combobox/combobox.cc b/views/controls/combobox/combobox.cc
index 0f8ee2bdee16e2e35578500faaaaa54071d3b460..c8bd106b6bda368f710736739c0ffc90b06ec752 100644
--- a/views/controls/combobox/combobox.cc
+++ b/views/controls/combobox/combobox.cc
@@ -126,9 +126,10 @@ void Combobox::GetAccessibleState(ui::AccessibleViewState* state) {
   state->count = model()->GetItemCount();
 }
 
-void Combobox::ViewHierarchyChanged(bool is_add, View* parent,
-                                    View* child) {
+void Combobox::ViewHierarchyChanged(bool is_add, View* parent, View* child) {
   if (is_add && !native_wrapper_ && GetWidget()) {
+    // The native wrapper's lifetime will be managed by the view hierarchy after
+    // we call AddChildView.
     native_wrapper_ = NativeComboboxWrapper::CreateWrapper(this);
     AddChildView(native_wrapper_->GetView());
   }