hack up frame latency measurement

Change-Id: I6d9a466a23285304f0e229a5649815636ab5d6af
diff --git a/services/surfaceflinger/LayerBase.h b/services/surfaceflinger/LayerBase.h
index 7f62145..0c1b228 100644
--- a/services/surfaceflinger/LayerBase.h
+++ b/services/surfaceflinger/LayerBase.h
@@ -205,7 +205,9 @@
     /** called with the state lock when the surface is removed from the
      *  current list */
     virtual void onRemoved() { };
-    
+
+    virtual void onLayerDisplayed() { };
+
     /** always call base class first */
     virtual void dump(String8& result, char* scratch, size_t size) const;
     virtual void shortDump(String8& result, char* scratch, size_t size) const;