fix mac all build

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2394943002

Review-Url: https://codereview.chromium.org/2394943002
diff --git a/tests/skia_test.cpp b/tests/skia_test.cpp
index a1c3c23..2b11e3a 100644
--- a/tests/skia_test.cpp
+++ b/tests/skia_test.cpp
@@ -96,7 +96,7 @@
               SkDebugf("\nFAILED: %s", failure.toString().c_str());
               fError = true;
           }
-          void* stats() { return fStats; }
+          void* stats() const override { return fStats; }
           void* fStats;
           bool fError;
           int fTestCount;