Make USE_EXTERNAL_POPUP_MENU local to content.

content/common/native_types.typemap

 # Copyright 2016 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.
 
 mojom = "//content/common/native_types.mojom"
 public_headers = [
   "//content/common/frame_owner_properties.h",
   "//content/common/frame_replication_state.h",
   "//content/common/resize_params.h",
   "//content/public/common/renderer_preferences.h",
   "//content/public/common/web_preferences.h",
   "//net/base/network_change_notifier.h",
   "//third_party/WebKit/public/web/WebPopupType.h",
 ]
 traits_headers = [
   "//content/common/frame_messages.h",
   "//content/common/view_messages.h",
   "//content/public/common/common_param_traits.h",
 ]
 public_deps = [
   # NOTE: These dependencies are here to satisfy gn check because
   # common_param_traits_macros.h and/or view_messages.h include their headers.
   # Although the mojo bindings target is configured to allow direct circular
   # includes from //content/common and //content/public/common, this isn't a
   # transitive allowance, so those targets' own public_deps aren't included in
   # the set of implied dependencies.
   "//cc/ipc",
+  "//content/common:features",
   "//media",
   "//media/base/ipc",
   "//net",
   "//ppapi/features",
   "//ui/accessibility",
   "//ui/base/ime:text_input_types",
   "//ui/gfx/ipc",
   "//ui/gfx/ipc/color",
   "//ui/gfx/ipc/skia",
   "//ui/surface",
   "//url/ipc:url_ipc",
 ]
 type_mappings = [
   "content.mojom.FrameOwnerProperties=content::FrameOwnerProperties",
   "content.mojom.FrameReplicationState=content::FrameReplicationState",
   "content.mojom.NetworkConnectionType=net::NetworkChangeNotifier::ConnectionType",
   "content.mojom.RendererPreferences=content::RendererPreferences",
   "content.mojom.ResizeParams=content::ResizeParams",
   "content.mojom.WebPopupType=blink::WebPopupType",
   "content.mojom.WebPreferences=content::WebPreferences",
 ]