Add Xlib support to viewer

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 "vk/GrVkDefines.h"
 
 #ifdef SK_DEBUG
 #define ENABLE_VK_LAYERS
 #endif
 
 struct GrVkInterface;
 
 enum GrVkExtensionFlags {
     kEXT_debug_report_GrVkExtensionFlag    = 0x0001,
     kNV_glsl_shader_GrVkExtensionFlag      = 0x0002,
     kKHR_surface_GrVkExtensionFlag         = 0x0004,
     kKHR_swapchain_GrVkExtensionFlag       = 0x0008,
     kKHR_win32_surface_GrVkExtensionFlag   = 0x0010,
     kKHR_android_surface_GrVkExtensionFlag = 0x0020,
-    kKHR_xlib_surface_GrVkExtensionFlag    = 0x0040,
+    kKHR_xcb_surface_GrVkExtensionFlag     = 0x0040,
 };
 
 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                          fGraphicsQueueIndex;
     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
     // If presentQueueIndex is non-NULL, will try to set up presentQueue as part of device
     // creation. canPresent() is a device-dependent function.
     static const GrVkBackendContext* Create(uint32_t* presentQueueIndex = nullptr,
-                    bool(*canPresent)(VkInstance, VkPhysicalDevice, uint32_t queueIndex) = nullptr);
+                    bool(*canPresent)(VkInstance, VkPhysicalDevice, uint32_t queueIndex,
+                                      void* platformData) = nullptr,
+                    void* platformData = nullptr);
 
     ~GrVkBackendContext() override;
 };
 
 #endif