rewrite density calculation code so it's understandable

Change-Id: I1016cd5fd75355abe4ab879d04f4849bd2dd4122
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 0098889..03e272d 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1680,13 +1680,15 @@
             "  transaction-flags         : %08x\n"
             "  refresh-rate              : %f fps\n"
             "  x-dpi                     : %f\n"
-            "  y-dpi                     : %f\n",
+            "  y-dpi                     : %f\n"
+            "  density                   : %f\n",
             mLastSwapBufferTime/1000.0,
             mLastTransactionTime/1000.0,
             mTransactionFlags,
             hw.getRefreshRate(),
             hw.getDpiX(),
-            hw.getDpiY());
+            hw.getDpiY(),
+            hw.getDensity());
     result.append(buffer);
 
     snprintf(buffer, SIZE, "  eglSwapBuffers time: %f us\n",