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

content/browser/compositor/gpu_process_transport_factory.cc

Index: content/browser/compositor/gpu_process_transport_factory.cc
diff --git a/content/browser/compositor/gpu_process_transport_factory.cc b/content/browser/compositor/gpu_process_transport_factory.cc
index 0b79d1480939960907eb75e3a2e704694efb7b13..2d6a2d6bac0914b55091cc7be27045f39e3474b1 100644
--- a/content/browser/compositor/gpu_process_transport_factory.cc
+++ b/content/browser/compositor/gpu_process_transport_factory.cc
@@ -48,6 +48,7 @@
 #include "gpu/command_buffer/common/mailbox.h"
 #include "gpu/ipc/client/gpu_channel_host.h"
 #include "gpu/ipc/host/gpu_memory_buffer_support.h"
+#include "gpu/vulkan/features.h"
 #include "services/service_manager/runner/common/client_util.h"
 #include "services/ui/public/cpp/gpu/context_provider_command_buffer.h"
 #include "third_party/khronos/GLES2/gl2.h"
@@ -95,7 +96,7 @@
 #include "gpu/ipc/common/gpu_surface_tracker.h"
 #endif
 
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
 #include "content/browser/compositor/vulkan_browser_compositor_output_surface.h"
 #endif
 
@@ -486,7 +487,7 @@ void GpuProcessTransportFactory::EstablishedGpuChannel(
   GpuVSyncControl* gpu_vsync_control = nullptr;
 
   std::unique_ptr<BrowserCompositorOutputSurface> display_output_surface;
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   std::unique_ptr<VulkanBrowserCompositorOutputSurface> vulkan_surface;
   if (vulkan_context_provider) {
     vulkan_surface.reset(new VulkanBrowserCompositorOutputSurface(