Add test configs for instanced rendering

src/gpu/GrDrawTarget.h

Index: src/gpu/GrDrawTarget.h
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index 18ad1c86993d03038ae402c9ab38a047cc10bdd0..02a77701347a8212254416c76127d1e46eca4bf1 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -139,10 +139,10 @@ public:
                      const SkIRect& srcRect,
                      const SkIPoint& dstPoint);
 
-    /**
-     * Gets the shape rendering object if it is supported on this platform.
-     */
-    gr_instanced::InstancedRendering* instancedRendering() const { return fInstancedRendering; }
+    gr_instanced::InstancedRendering* instancedRendering() const {
+        SkASSERT(fInstancedRendering);
+        return fInstancedRendering;
+    }
 
 private:
     friend class GrDrawingManager; // for resetFlag & TopoSortTraits