Revise layer, extension and feature setup for Vulkan

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;
 
+enum GrVkExtensionFlags {
+    kEXT_debug_report_GrVkExtensionFlag = 0x0001,
+    kNV_glsl_shader_GrVkExtensionFlag   = 0x0002,
+};
+
+enum GrVkFeatureFlags {
+    kGeometryShader_GrVkFeatureFlag    = 0x0001,
+    kDualSrcBlend_GrVkFeatureFlag      = 0x0002,
+    kSampleRateShading_GrVkFeatureFlag = 0x0004,
+};
+
 // 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;
+    uint32_t                          fMinAPIVersion;
+    uint32_t                          fExtensions;
+    uint32_t                          fFeatures;
     SkAutoTUnref<const GrVkInterface> fInterface;
 
     // Helper function to create the default Vulkan objects needed by the GrVkGpu object
     static const GrVkBackendContext* Create();
 
     ~GrVkBackendContext() override;
 };
 
 #endif