share code around animating the rotating cube

Change-Id: I90e0918b1ce6df7f54fae67916754289eb9a263b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272638
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/samplecode/Sample3D.cpp b/samplecode/Sample3D.cpp
index b2fd783..29de2da 100644
--- a/samplecode/Sample3D.cpp
+++ b/samplecode/Sample3D.cpp
@@ -218,6 +218,8 @@
         fAngle = 0;
         fPrevAngle = 1234567;
     }
+
+    bool isAnimating() const { return fAngleSpeed != 0; }
 };
 
 class SampleCubeBase : public Sample3DView {
@@ -353,8 +355,7 @@
     }
 
     bool onAnimate(double nanos) override {
-        // handle fling
-        return this->INHERITED::onAnimate(nanos);
+        return fRotateAnimator.isAnimating();
     }
 
 private: