Revise WSI setup.

include/gpu/vk/GrVkBackendContext.h

Index: include/gpu/vk/GrVkBackendContext.h
diff --git a/include/gpu/vk/GrVkBackendContext.h b/include/gpu/vk/GrVkBackendContext.h
index 82a9f94bccd46f34cb44ebc4105a4ef05247e0a1..d33466ca25e0b0f62b1bf01b99c3ae1dc2f14a14 100644
--- a/include/gpu/vk/GrVkBackendContext.h
+++ b/include/gpu/vk/GrVkBackendContext.h
@@ -45,14 +45,17 @@ struct GrVkBackendContext : public SkRefCnt {
     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;
 };