Move the supervised user error page to a component

components/supervised_user_error_page/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.
+
+source_set("supervised_user_error_page") {
+  sources = [
+    "supervised_user_error_page.cc",
+    "supervised_user_error_page.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/resources",
+    "//components/strings",
+    "//ui/base",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "supervised_user_error_page_unittest.cc",
+  ]
+  deps = [
+    ":supervised_user_error_page",
+    "//base",
+    "//base/test:test_support",
+    "//components/resources",
+    "//components/strings",
+    "//testing/gmock",
+    "//testing/gtest",
+    "//ui/base",
+  ]
+}