Began logging more gpu stats from nanobench

BUG=skia:

Review URL: https://codereview.chromium.org/1489033004
diff --git a/bench/Benchmark.h b/bench/Benchmark.h
index a403a6e..30c7aa9 100644
--- a/bench/Benchmark.h
+++ b/bench/Benchmark.h
@@ -124,6 +124,8 @@
         this->perCanvasPostDraw(canvas);
     }
 
+    virtual void getGpuStats(SkCanvas*, SkTArray<SkString>* keys, SkTArray<double>* values) {}
+
 protected:
     virtual void setupPaint(SkPaint* paint);