Move debug_devtools to a buildflag_header.

chrome/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/buildflag_header.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/features.gni")
 import("//build/config/locales.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/config/win/console_app.gni")
 import("//build/config/win/manifest.gni")
 import("//build/toolchain/toolchain.gni")
 import("//chrome/chrome_paks.gni")
 import("//chrome/common/features.gni")
 import("//chrome/process_version_rc_template.gni")
 import("//ppapi/features/features.gni")
+import("//third_party/WebKit/public/public_features.gni")
 import("//third_party/widevine/cdm/widevine.gni")
 import("//tools/resources/generate_resource_whitelist.gni")
 import("//v8/gni/v8.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 } else if (is_mac) {
   import("//build/compiled_action.gni")
   import("//build/config/mac/rules.gni")
   import("//build/config/mac/symbols.gni")
@@ skipping 1544 matching lines @@
       "//chrome/app/theme/$branding_path_component/product_logo_48.png",
       "//chrome/tools/build/linux/chrome-wrapper",
       "//third_party/xdg-utils/scripts/xdg-mime",
       "//third_party/xdg-utils/scripts/xdg-settings",
     ]
     outputs = [
       "$root_out_dir/{{source_file_part}}",
     ]
   }
 }