CppTools: Garbage collect if the last CppEditor is closed

Task-number: QTCREATORBUG-9828

Change-Id: Ie0ef9757cedb772702e49542b58d5b589506aa9e
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpptoolsplugin.h

@@ -187,6 +187,7 @@ private slots:
     void test_modelmanager_refresh_2();
     void test_modelmanager_snapshot_after_two_projects();
     void test_modelmanager_extraeditorsupport_uiFiles();
+    void test_modelmanager_gc_if_last_cppeditor_closed();
 
 private:
     void test_completion();