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

cc/output/vulkan_in_process_context_provider.cc

Index: cc/output/vulkan_in_process_context_provider.cc
diff --git a/cc/output/vulkan_in_process_context_provider.cc b/cc/output/vulkan_in_process_context_provider.cc
index 9d602c42450162bf5864e93e36b66e184f2fd4a4..f8a3b21025a10f6fac57162cbf263a65fdb47a92 100644
--- a/cc/output/vulkan_in_process_context_provider.cc
+++ b/cc/output/vulkan_in_process_context_provider.cc
@@ -3,17 +3,18 @@
 // found in the LICENSE file.
 
 #include "cc/output/vulkan_in_process_context_provider.h"
+#include "gpu/vulkan/features.h"
 
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
 #include "gpu/vulkan/vulkan_device_queue.h"
 #include "gpu/vulkan/vulkan_implementation.h"
-#endif  // defined(ENABLE_VULKAN)
+#endif  // BUILDFLAG(ENABLE_VULKAN)
 
 namespace cc {
 
 scoped_refptr<VulkanInProcessContextProvider>
 VulkanInProcessContextProvider::Create() {
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   if (!gpu::VulkanSupported())
     return nullptr;
 
@@ -28,7 +29,7 @@ VulkanInProcessContextProvider::Create() {
 }
 
 bool VulkanInProcessContextProvider::Initialize() {
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   DCHECK(!device_queue_);
   std::unique_ptr<gpu::VulkanDeviceQueue> device_queue(
       new gpu::VulkanDeviceQueue);
@@ -47,7 +48,7 @@ bool VulkanInProcessContextProvider::Initialize() {
 }
 
 void VulkanInProcessContextProvider::Destroy() {
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   if (device_queue_) {
     device_queue_->Destroy();
     device_queue_.reset();
@@ -56,7 +57,7 @@ void VulkanInProcessContextProvider::Destroy() {
 }
 
 gpu::VulkanDeviceQueue* VulkanInProcessContextProvider::GetDeviceQueue() {
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   return device_queue_.get();
 #else
   return nullptr;