add const qualifiers

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52414 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/stopwatch.h

@@ -64,7 +64,7 @@ public:
         of
         Pause().
     */
-    long Time();
+    long Time() const;
 };