Make USE_EXTERNAL_POPUP_MENU local to content.

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")
@@ skipping 45 matching lines @@
     "//content/browser/background_sync:background_sync_proto",
     "//content/browser/cache_storage:cache_storage_proto",
     "//content/browser/devtools:protocol_sources",
     "//content/browser/devtools:resources",
     "//content/browser/dom_storage:local_storage_proto",
     "//content/browser/notifications:notification_proto",
     "//content/browser/payments:payment_app_proto",
     "//content/browser/service_worker:service_worker_proto",
     "//content/browser/speech/proto",
     "//content/common",
+    "//content/common:features",
     "//content/public/common:common_sources",
     "//crypto",
     "//device/battery",
     "//device/battery:mojo_bindings",
     "//device/bluetooth",
     "//device/gamepad",
     "//device/generic_sensor",
     "//device/geolocation",
     "//device/geolocation/public/interfaces",
     "//device/nfc:mojo_bindings",
@@ skipping 1962 matching lines @@
   if (!is_component_build) {
     public_deps = [
       ":browser",
     ]
   } else {
     public_deps = [
       "//third_party/leveldatabase",
     ]
   }
 }