Update platform classes to use OVERRIDE / FINAL when needed

Source/platform/SharedTimer.h

Index: Source/platform/SharedTimer.h
diff --git a/Source/platform/SharedTimer.h b/Source/platform/SharedTimer.h
index e5386fd5cbf69c9ef40ca80bbfabaefb70186cf7..2d5a1c10df440cde77d8804cd9398afb10912edd 100644
--- a/Source/platform/SharedTimer.h
+++ b/Source/platform/SharedTimer.h
@@ -54,17 +54,17 @@ PLATFORM_EXPORT void stopSharedTimer();
 
 class PLATFORM_EXPORT MainThreadSharedTimer : public SharedTimer {
 public:
-    virtual void setFiredFunction(void (*function)())
+    virtual void setFiredFunction(void (*function)()) OVERRIDE
     {
         setSharedTimerFiredFunction(function);
     }
 
-    virtual void setFireInterval(double interval)
+    virtual void setFireInterval(double interval) OVERRIDE
     {
         setSharedTimerFireInterval(interval);
     }
 
-    virtual void stop()
+    virtual void stop() OVERRIDE
     {
         stopSharedTimer();
     }