allow GMs to animate

BUG=skia:

Review URL: https://codereview.chromium.org/888283002
diff --git a/samplecode/GMSampleView.h b/samplecode/GMSampleView.h
index c781cd0..a03628e 100644
--- a/samplecode/GMSampleView.h
+++ b/samplecode/GMSampleView.h
@@ -70,6 +70,10 @@
         fGM->drawBackground(canvas);
     }
 
+    bool onAnimatePulse(SkMSec curr, SkMSec prev) SK_OVERRIDE {
+        return fGM->animatePulse(curr, prev);
+    }
+
 private:
     GM* fGM;
     typedef SampleView INHERITED;