surfaceflinger: add frame duration logging

Change-Id: Ib414a45e7e191f23a2726cbbbeb606e9ce68a3b5
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 21d523b..7099b35 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -132,6 +132,10 @@
     friend class Layer;
     friend class SurfaceTextureLayer;
 
+    // This value is specified in number of frames.  Log frame stats at most
+    // every half hour.
+    enum { LOG_FRAME_STATS_PERIOD =  30*60*60 };
+
     // We're reference counted, never destroy SurfaceFlinger directly
     virtual ~SurfaceFlinger();
 
@@ -392,6 +396,8 @@
             const sp<const DisplayDevice>& hw,
             uint32_t minLayerZ, uint32_t maxLayerZ);
 
+    void logFrameStats();
+
     /* ------------------------------------------------------------------------
      * Attributes
      */