Revert of Remove enable_vulkan from build/config, and move it to the buildflag_header system.

cc/output/vulkan_in_process_context_provider.cc

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/vulkan_in_process_context_provider.h"
-#include "gpu/vulkan/features.h"
 
-#if BUILDFLAG(ENABLE_VULKAN)
+#if defined(ENABLE_VULKAN)
 #include "gpu/vulkan/vulkan_device_queue.h"
 #include "gpu/vulkan/vulkan_implementation.h"
-#endif  // BUILDFLAG(ENABLE_VULKAN)
+#endif  // defined(ENABLE_VULKAN)
 
 namespace cc {
 
 scoped_refptr<VulkanInProcessContextProvider>
 VulkanInProcessContextProvider::Create() {
-#if BUILDFLAG(ENABLE_VULKAN)
+#if defined(ENABLE_VULKAN)
   if (!gpu::VulkanSupported())
     return nullptr;
 
   scoped_refptr<VulkanInProcessContextProvider> context_provider(
       new VulkanInProcessContextProvider);
   if (!context_provider->Initialize())
     return nullptr;
   return context_provider;
 #else
   return nullptr;
 #endif
 }
 
 bool VulkanInProcessContextProvider::Initialize() {
-#if BUILDFLAG(ENABLE_VULKAN)
+#if defined(ENABLE_VULKAN)
   DCHECK(!device_queue_);
   std::unique_ptr<gpu::VulkanDeviceQueue> device_queue(
       new gpu::VulkanDeviceQueue);
   if (!device_queue->Initialize(
           gpu::VulkanDeviceQueue::GRAPHICS_QUEUE_FLAG |
           gpu::VulkanDeviceQueue::PRESENTATION_SUPPORT_QUEUE_FLAG)) {
     device_queue->Destroy();
     return false;
   }
 
   device_queue_ = std::move(device_queue);
   return true;
 #else
   return false;
 #endif
 }
 
 void VulkanInProcessContextProvider::Destroy() {
-#if BUILDFLAG(ENABLE_VULKAN)
+#if defined(ENABLE_VULKAN)
   if (device_queue_) {
     device_queue_->Destroy();
     device_queue_.reset();
   }
 #endif
 }
 
 gpu::VulkanDeviceQueue* VulkanInProcessContextProvider::GetDeviceQueue() {
-#if BUILDFLAG(ENABLE_VULKAN)
+#if defined(ENABLE_VULKAN)
   return device_queue_.get();
 #else
   return nullptr;
 #endif
 }
 
 VulkanInProcessContextProvider::VulkanInProcessContextProvider() {}
 
 VulkanInProcessContextProvider::~VulkanInProcessContextProvider() {
   Destroy();
 }
 
 }  // namespace cc