function _updateEditorOverwriteMode(event) {
        var editor = EditorManager.getActiveEditor(),
            newstate = !editor._codeMirror.state.overwrite;

        // update label with no transition
        _updateOverwriteLabel(event, editor, newstate, true);
        editor.toggleOverwrite(newstate);
    }
Update insert/overwrite indicator
@param {Event} event (unused)