Make sure that Vulkan debug callback ptr is non-null.

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 8b8883bd047d44977bf6d12dae31b62a14a9a712..4dc1f526750e23e84bb427952a77c7d52b52a62e 100644
--- a/src/gpu/vk/GrVkGpu.h
+++ b/src/gpu/vk/GrVkGpu.h
@@ -208,9 +208,6 @@ private:
 
     // These Vulkan objects are provided by the client, and also stored in fBackendContext.
     // They're copied here for convenient access.
-#ifdef ENABLE_VK_LAYERS
-    VkInstance                             fVkInstance;
-#endif
     VkDevice                               fDevice;
     VkQueue                                fQueue;    // Must be Graphics queue
 
@@ -222,7 +219,7 @@ private:
 
 #ifdef ENABLE_VK_LAYERS
     // For reporting validation layer errors
-    VkDebugReportCallbackEXT               fCallback;
+	VkDebugReportCallbackEXT               fCallback;

[djsollen, 2016/05/02 19:17:44]

spaces not tabs.

[jvanverth1, 2016/05/02 19:56:33]

Done.

 #endif
 
     // Shaderc compiler used for compiling glsl in spirv. We only want to create the compiler once