Fix interface validation in Vulkan.

TBR=bsalomon@google.com

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3176

Change-Id: Ifad3249e6839e9b4aa34792646b2d54ff9304da7
Reviewed-on: https://skia-review.googlesource.com/3176
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index 60a8763..0eb8241 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -80,6 +80,10 @@
         vkBackendContext->ref();
     }
 
+    if (!vkBackendContext->fInterface->validate(vkBackendContext->fExtensions)) {
+        return nullptr;
+    }
+
     return new GrVkGpu(context, options, vkBackendContext);
 }