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

content/browser/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//gpu/vulkan/features.gni")
 import("//media/media_options.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
 import("//third_party/WebKit/public/public_features.gni")
 import("//tools/ipc_fuzzer/ipc_fuzzer.gni")
 
 source_set("browser") {
   # Only the public target should depend on this. All other targets (even
   # internal content ones) should depend on the public one.
   visibility = [
@@ skipping 59 matching lines @@
     "//device/screen_orientation/public/interfaces",
     "//device/sensors",
     "//device/vibration",
     "//device/vr",
     "//device/wake_lock",
     "//google_apis",
     "//gpu",
     "//gpu/command_buffer/client:gles2_implementation",
     "//gpu/command_buffer/client:gles2_interface",
     "//gpu/ipc/host",
-    "//gpu/vulkan:features",
     "//ipc",
     "//media",
     "//media/capture",
     "//media/capture/mojo:image_capture",
     "//media/gpu/ipc/client",
     "//media/midi",
     "//media/midi:mojo",
     "//media/mojo/interfaces",
     "//mojo/common",
     "//mojo/edk/system",
@@ skipping 1938 matching lines @@
   if (!is_component_build) {
     public_deps = [
       ":browser",
     ]
   } else {
     public_deps = [
       "//third_party/leveldatabase",
     ]
   }
 }