Revise WSI setup.

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
 
@@ skipping 27 matching lines @@
 // 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                          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
-    static const GrVkBackendContext* Create();
+    // 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);
 
     ~GrVkBackendContext() override;
 };
 
 #endif