Add header comment for Vulkan swapchain block

The swapchain function pointer block is currently missing a header
comment.

This CL adds it.

BUG=856360

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Iade801831fef5a4502f2c66852182f22ef4619aa
Reviewed-on: https://chromium-review.googlesource.com/1114220Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570221}

gpu/vulkan/generate_bindings.py

@@ -163,6 +163,11 @@ struct VulkanFunctionPointers {
   for func in command_buffer_functions:
     file.write('  PFN_' + func['name'] + ' ' + func['name'] + ' = nullptr;\n')
 
+  file.write("""\
+
+  // Swapchain functions
+""")
+
   for func in swapchain_functions:
     file.write('  PFN_' + func['name'] + ' ' + func['name'] + ' = nullptr;\n')
 

gpu/vulkan/vulkan_function_pointers.h

@@ -104,6 +104,8 @@ struct VulkanFunctionPointers {
   PFN_vkCmdPipelineBarrier vkCmdPipelineBarrier = nullptr;
   PFN_vkEndCommandBuffer vkEndCommandBuffer = nullptr;
   PFN_vkResetCommandBuffer vkResetCommandBuffer = nullptr;
+
+  // Swapchain functions
   PFN_vkAcquireNextImageKHR vkAcquireNextImageKHR = nullptr;
   PFN_vkCreateSwapchainKHR vkCreateSwapchainKHR = nullptr;
   PFN_vkDestroySwapchainKHR vkDestroySwapchainKHR = nullptr;