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

views/controls/combobox/combobox.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "views/controls/combobox/combobox.h"
 
 #include "base/logging.h"
 #include "base/utf_string_conversions.h"
 #include "ui/base/accessibility/accessible_view_state.h"
 #include "ui/base/keycodes/keyboard_codes.h"
@@ skipping 108 matching lines @@
 }
 
 void Combobox::GetAccessibleState(ui::AccessibleViewState* state) {
   state->role = ui::AccessibilityTypes::ROLE_COMBOBOX;
   state->name = accessible_name_;
   state->value = model_->GetItemAt(selected_item_);
   state->index = selected_item();
   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());
   }
 }
 
 std::string Combobox::GetClassName() const {
   return kViewClassName;
 }
 
 }  // namespace views