Move wxControl::GetCompositeControlsDefaultAttributes() from MSW to common.

This function is not MSW-specific and should be used in generic implementation
of controls such as wxListCtrl, wxTreeCtrl and wxDataViewCtrl. Even if it is
needed by MSW only now, move it to the common code to avoid #ifdefs in these
controls code.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62151 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/control.h

@@ -131,6 +131,13 @@ public:
     static int FindAccelIndex(const wxString& label,
                               wxString *labelOnly = NULL);
 
+    // this is a helper for the derived class GetClassDefaultAttributes()
+    // implementation: it returns the right colours for the classes which
+    // contain something else (e.g. wxListBox, wxTextCtrl, ...) instead of
+    // being simple controls (such as wxButton, wxCheckBox, ...)
+    static wxVisualAttributes
+        GetCompositeControlsDefaultAttributes(wxWindowVariant variant);
+
 protected:
     // choose the default border for this window
     virtual wxBorder GetDefaultBorder() const;