This CL replaces user_manager::UserID with AccountId.

ash/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("//testing/test.gni")
 
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("ash.gyp") ],
                           "scope",
                           [ "ash.gyp" ])
 
 component("ash") {
   sources = gypi_values.ash_sources
 
   configs += [ "//build/config:precompiled_headers" ]
   defines = [ "ASH_IMPLEMENTATION" ]
 
   public_deps = [
     "//ash/resources",
     "//ash/strings",
   ]
   deps = [
     "//base",
     "//base:i18n",
     "//base/third_party/dynamic_annotations",
     "//cc",
     "//components/device_event_log",
+    "//components/signin/core/account_id",
     "//components/user_manager",
     "//components/wallpaper",
     "//content/public/browser",
     "//media",
     "//net",
     "//skia",
     "//third_party/icu",
     "//ui/accessibility",
     "//ui/app_list",
     "//ui/aura",
@@ skipping 242 matching lines @@
 
   deps = [
     ":ash",
     ":ash_with_content",
     ":test_support",
     "//ash/resources",
     "//ash/strings",
     "//base",
     "//base/allocator",
     "//base/test:test_support",
+    "//components/signin/core/account_id",
     "//components/user_manager",
     "//content/public/browser",
     "//content/test:test_support",
     "//skia",
     "//testing/gtest",
     "//third_party/icu",
     "//ui/accessibility",
     "//ui/aura",
     "//ui/aura:test_support",
     "//ui/base",
@@ skipping 98 matching lines @@
     configs += [ "//build/config/win:windowed" ]
     deps += [ "//sandbox" ]
   }
 
   if (is_chromeos) {
     deps += [ "//device/bluetooth" ]
   }
 }
 # When adding support for isolates, please have a look at run-time dependencies
 # in the ash_unittests_run target in ash.gyp.