ui/base/models: Add protected virtual destructor to ComboboxModel.

The use of a protected virtual destructor is to prevent the destruction of a
derived object via a base-class pointer.

That's it, ComboboxModel should only be deleted through derived class.

Example 1:

class FooComboboxModel : public ComboboxModel {
};

ComboboxModel* model = new FooComboboxModel;
delete model;  // It should prevent this situation!

Also, a protected virtual destructor makes it clear that someone else owns the
object.

Example 2:

class Foo {
 public:
  void SetModel(ComboboxModel* model);
};

If you see that the model has a protected destructor, you know Foo doesn't own
|model|.

R=sky@chromium.org

Review URL: https://chromiumcodereview.appspot.com/9817007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@128132 0039d316-1c4b-4281-b951-d872f2087c98

0 files changed, 0 insertions, 0 deletions