CppTools: Get OverviewModel from model manager

Move ownership and add the placeholder for future clang based
OverviewModel.

Change-Id: Ia44d2c1d0db59b40239d1f7934bf37a02e4b14e6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cppmodelmanagersupportinternal.cpp

@@ -27,6 +27,7 @@
 #include "cppmodelmanagersupportinternal.h"
 #include "cppfollowsymbolundercursor.h"
 #include "cpphoverhandler.h"
+#include "cppoverviewmodel.h"
 #include "cpprefactoringengine.h"
 #include "builtineditordocumentprocessor.h"
 
@@ -89,3 +90,8 @@ RefactoringEngineInterface &ModelManagerSupportInternal::refactoringEngineInterf
 {
     return *m_refactoringEngine;
 }
+
+std::unique_ptr<AbstractOverviewModel> ModelManagerSupportInternal::createOverviewModel()
+{
+    return std::make_unique<CppTools::OverviewModel>();
+}