Use transfer buffer for BatchAtlas texture copies

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 5872f18671972415e5d595472fa51b57f1e0c9ad..5129e75af68bd7290a1fc6f11848acebf61904db 100644
--- a/src/gpu/vk/GrVkGpu.h
+++ b/src/gpu/vk/GrVkGpu.h
@@ -153,7 +153,7 @@ private:
     bool onTransferPixels(GrSurface*,
                           int left, int top, int width, int height,
                           GrPixelConfig config, GrBuffer* transferBuffer,
-                          size_t offset, size_t rowBytes) override { return false; }
+                          size_t offset, size_t rowBytes) override;
 
     void onResolveRenderTarget(GrRenderTarget* target) override {}