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

cc/output/vulkan_in_process_context_provider.h

 // Copyright 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.
 
 #ifndef CC_OUTPUT_VULKAN_IN_PROCESS_CONTEXT_PROVIDER_H_
 #define CC_OUTPUT_VULKAN_IN_PROCESS_CONTEXT_PROVIDER_H_
 
 #include <memory>
 
 #include "cc/base/cc_export.h"
 #include "cc/output/vulkan_context_provider.h"
+#include "gpu/vulkan/features.h"
 
 namespace gpu {
 class VulkanDeviceQueue;
 }
 
 namespace cc {
 
 class CC_EXPORT VulkanInProcessContextProvider : public VulkanContextProvider {
  public:
   static scoped_refptr<VulkanInProcessContextProvider> Create();
 
   bool Initialize();
   void Destroy();
 
   // VulkanContextProvider implementation
   gpu::VulkanDeviceQueue* GetDeviceQueue() override;
 
  protected:
   VulkanInProcessContextProvider();
   ~VulkanInProcessContextProvider() override;
 
  private:
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   std::unique_ptr<gpu::VulkanDeviceQueue> device_queue_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(VulkanInProcessContextProvider);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_VULKAN_IN_PROCESS_CONTEXT_PROVIDER_H_