vulkan: Add KHR_swapchain_front_buffered to header and api

This is tacked in by hand since the extension MR hasn't landed yet in
the Khronos repo.

Test: build
Change-Id: Iccfce0032f27fca982cdb4e9ee414df036f01613
diff --git a/vulkan/api/vulkan.api b/vulkan/api/vulkan.api
index df45c20..1023182 100644
--- a/vulkan/api/vulkan.api
+++ b/vulkan/api/vulkan.api
@@ -150,6 +150,9 @@
 @extension("VK_NVX_device_generated_commands") define VK_NVX_DEVICE_GENERATED_COMMANDS_SPEC_VERSION 1
 @extension("VK_NVX_device_generated_commands") define VK_NVX_DEVICE_GENERATED_COMMANDS_EXTENSION_NAME "VK_NVX_device_generated_commands"
 
+@extension("VK_KHR_swapchain_front_buffered") define VK_KHR_SWAPCHAIN_FRONT_BUFFERED_SPEC_VERSION 2
+@extension("VK_KHR_swapchain_front_buffered") define VK_KHR_SWAPCHAIN_FRONT_BUFFERED_EXTENSION_NAME "VK_KHR_swapchain_front_buffered"
+
 
 
 /////////////
@@ -924,6 +927,10 @@
     VK_PRESENT_MODE_MAILBOX_KHR                             = 0x00000001,
     VK_PRESENT_MODE_FIFO_KHR                                = 0x00000002,
     VK_PRESENT_MODE_FIFO_RELAXED_KHR                        = 0x00000003,
+    //@extension("VK_KHR_swapchain_front_buffered")
+    VK_PRESENT_MODE_FRONT_BUFFERED_DEMAND_REFRESH_KHR       = 1000111000,
+    //@extension("VK_KHR_swapchain_front_buffered")
+    VK_PRESENT_MODE_FRONT_BUFFERED_CONTINUOUS_REFRESH_KHR   = 1000111001,
 }
 
 @extension("VK_KHR_surface")
@@ -6109,6 +6116,13 @@
         VkDeviceGeneratedCommandsLimitsNVX*         pLimits) {
 }
 
+@extension("VK_KHR_swapchain_front_buffered")
+cmd VkResult vkGetSwapchainStatusKHR(
+        VkDevice                                    device,
+        VkSwapchainKHR                              swapchain) {
+    return ?
+}
+
 
 ////////////////
 // Validation //