GrVkGpu initialization cleanup.

include/gpu/vk/GrVkBackendContext.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrVkBackendContext_DEFINED
+#define GrVkBackendContext_DEFINED
+
+#include "SkRefCnt.h"
+
+#include "vulkan/vulkan.h"
+
+#ifdef SK_DEBUG
+#define ENABLE_VK_LAYERS
+#endif
+
+struct GrVkInterface;
+
+// The BackendContext contains all of the base Vulkan objects needed by the GrVkGpu. The assumption
+// is that the client will set these up and pass them to the GrVkGpu constructor. The VkDevice
+// created must support at least one graphics queue, which is passed in as well. 
+// The QueueFamilyIndex must match the family of the given queue. It is needed for CommandPool 
+// creation, and any GrBackendObjects handed to us (e.g., for wrapped textures) need to be created
+// in or transitioned to that family.
+struct GrVkBackendContext : public SkRefCnt {
+    VkInstance                        fInstance;
+    VkPhysicalDevice                  fPhysicalDevice;
+    VkDevice                          fDevice;
+    VkQueue                           fQueue;
+    uint32_t                          fQueueFamilyIndex;
+    SkAutoTUnref<const GrVkInterface> fInterface;
+
+    // Helper function to create the default Vulkan objects needed by the GrVkGpu object
+    static const GrVkBackendContext* Create();
+
+    ~GrVkBackendContext() override;
+};
+
+#endif