Began logging more gpu stats from nanobench

BUG=skia:

Review URL: https://codereview.chromium.org/1489033004
diff --git a/bench/SKPBench.h b/bench/SKPBench.h
index 89c9a36..1f34a00 100644
--- a/bench/SKPBench.h
+++ b/bench/SKPBench.h
@@ -28,6 +28,8 @@
         return fDoLooping ? defaultLoops : 1;
     }
 
+    void getGpuStats(SkCanvas*, SkTArray<SkString>* keys, SkTArray<double>* values) override;
+
 protected:
     const char* onGetName() override;
     const char* onGetUniqueName() override;