Add stub for new method to GrVkGpu

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 5bffdfdf93f8739f77929d656fbcea7e765f12b1..e04095ea71a59a9d896729e6dd4c10b5dcb47d1b 100644
--- a/src/gpu/vk/GrVkGpu.h
+++ b/src/gpu/vk/GrVkGpu.h
@@ -137,6 +137,11 @@ private:
 
     GrRenderTarget* onWrapBackendRenderTarget(const GrBackendRenderTargetDesc&,
                                               GrWrapOwnership) override;
+    GrRenderTarget* onWrapBackendTextureAsRenderTarget(const GrBackendTextureDesc&,
+                                                       GrWrapOwnership) override {
+        SkDebugf("onWrapBackendTextureAsRenderTarget not yet implemented for Vulkan\n");
+        return NULL;
+    }
 
     GrVertexBuffer* onCreateVertexBuffer(size_t size, bool dynamic) override;
     GrIndexBuffer* onCreateIndexBuffer(size_t size, bool dynamic) override;