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

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index 1762d79995c482269975164203244b9f2aa5185a..cce68adc346f637ef0bc16d182e3d510e23e5d9a 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -93,6 +93,7 @@
 #include "device/battery/battery_status_service.h"
 #include "device/gamepad/gamepad_service.h"
 #include "device/sensors/device_sensor_service.h"
+#include "gpu/vulkan/features.h"
 #include "media/audio/audio_system_impl.h"
 #include "media/base/media.h"
 #include "media/base/user_input_monitor.h"
@@ -206,7 +207,7 @@
 #include "crypto/nss_util.h"
 #endif
 
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
 #include "gpu/vulkan/vulkan_implementation.h"
 #endif
 
@@ -1430,7 +1431,7 @@ int BrowserMainLoop::BrowserThreadsStarted() {
   base::PlatformThread::SetCurrentThreadPriority(base::ThreadPriority::DISPLAY);
 #endif
 
-#if defined(ENABLE_VULKAN)
+#if BUILDFLAG(ENABLE_VULKAN)
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnableVulkan)) {
     gpu::InitializeVulkan();