Allow overriding print preview frame creation in docview.

Add a virtual wxDocManager::CreatePreviewFrame() which can be overridden to
customize the print preview used by docview framework.

Closes #11390.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63757 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/docview.h

@@ -516,6 +516,24 @@ public:
     */
     wxList& GetTemplates();
 
+    /**
+        Create the frame used for print preview.
+
+        This method can be overridden if you need to change the behaviour or
+        appearance of the preview window. By default, a standard wxPreviewFrame
+        is created.
+
+        @since 2.9.1
+
+        @param preview The associated preview object.
+        @param parent The parent window for the frame.
+        @param title The suggested title for the print preview frame.
+        @return A new print preview frame, must not return @NULL.
+    */
+    virtual wxPreviewFrame* CreatePreviewFrame(wxPrintPreviewBase* preview,
+                                               wxWindow* parent,
+                                               const wxString& title);
+
     /**
         Initializes data; currently just calls OnCreateFileHistory().