Display average frame duration & renderengine duration in timestats dump

Bug: none
Test: atest libsurfaceflinger_unittest
Test: adb shell su root dumpsys SurfaceFlinger --timestats -dump -maxlayers 0
Change-Id: I360858a1c06b90c8197ee705465d56531aa99e98
diff --git a/services/surfaceflinger/TimeStats/timestatsproto/TimeStatsHelper.cpp b/services/surfaceflinger/TimeStats/timestatsproto/TimeStatsHelper.cpp
index 1c910aa..e2f85cc 100644
--- a/services/surfaceflinger/TimeStats/timestatsproto/TimeStatsHelper.cpp
+++ b/services/surfaceflinger/TimeStats/timestatsproto/TimeStatsHelper.cpp
@@ -114,8 +114,14 @@
     StringAppendF(&result, "totalP2PTime = %" PRId64 " ms\n", presentToPresent.totalTime());
     StringAppendF(&result, "presentToPresent histogram is as below:\n");
     result.append(presentToPresent.toString());
+    const float averageFrameDuration = frameDuration.averageTime();
+    StringAppendF(&result, "averageFrameDuration = %.3f ms\n",
+                  std::isnan(averageFrameDuration) ? 0.0f : averageFrameDuration);
     StringAppendF(&result, "frameDuration histogram is as below:\n");
     result.append(frameDuration.toString());
+    const float averageRenderEngineTiming = renderEngineTiming.averageTime();
+    StringAppendF(&result, "averageRenderEngineTiming = %.3f ms\n",
+                  std::isnan(averageRenderEngineTiming) ? 0.0f : averageRenderEngineTiming);
     StringAppendF(&result, "renderEngineTiming histogram is as below:\n");
     result.append(renderEngineTiming.toString());
     const auto dumpStats = generateDumpStats(maxLayers);