Add test configs for instanced rendering

src/gpu/vk/GrVkGpu.h

Index: src/gpu/vk/GrVkGpu.h
diff --git a/src/gpu/vk/GrVkGpu.h b/src/gpu/vk/GrVkGpu.h
index a0bed3bcbe93aa45711bd8dca242e53b5b8f1082..1554115905d351e371ec188ff077aacaa6169764 100644
--- a/src/gpu/vk/GrVkGpu.h
+++ b/src/gpu/vk/GrVkGpu.h
@@ -182,6 +182,8 @@ private:
     GrBuffer* onCreateBuffer(size_t size, GrBufferType type, GrAccessPattern,
                              const void* data) override;
 
+    gr_instanced::InstancedRendering* onCreateInstancedRendering() override { return nullptr; }
+
     bool onReadPixels(GrSurface* surface,
                       int left, int top, int width, int height,
                       GrPixelConfig,