automated changes: many (pure) virtual specifiers added

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56276 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/html/htmlfilt.h

@@ -29,12 +29,12 @@ public:
         Returns @true if this filter is capable of reading file @e file.
         Example:
     */
-    bool CanRead(const wxFSFile& file);
+    virtual bool CanRead(const wxFSFile& file) const = 0;
 
     /**
         Reads the file and returns string with HTML document.
         Example:
     */
-    wxString ReadFile(const wxFSFile& file);
+    virtual wxString ReadFile(const wxFSFile& file) const = 0;
 };