Convert TrackedPreferenceValidationDelegate into a mojo interface.

components/user_prefs/tracked/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.
 
 static_library("user_prefs_tracked") {
   sources = [
     "device_id.h",
     "device_id_mac.cc",
     "device_id_stub.cc",
     "device_id_win.cc",
@@ skipping 16 matching lines @@
     "registry_hash_store_contents_win.h",
     "segregated_pref_store.cc",
     "segregated_pref_store.h",
     "tracked_atomic_preference.cc",
     "tracked_atomic_preference.h",
     "tracked_preference.h",
     "tracked_preference_helper.cc",
     "tracked_preference_helper.h",
     "tracked_preference_histogram_names.cc",
     "tracked_preference_histogram_names.h",
-    "tracked_preference_validation_delegate.h",
     "tracked_preferences_migration.cc",
     "tracked_preferences_migration.h",
     "tracked_split_preference.cc",
     "tracked_split_preference.h",
   ]
 
   if (is_win || is_mac) {
     sources -= [ "device_id_stub.cc" ]
   }
 
   # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
+  public_deps = [
+    "//services/preferences/public/interfaces",
+  ]
+
   deps = [
     "//base:base",
     "//components/pref_registry",
     "//components/prefs",
     "//crypto:crypto",
   ]
 }
 
 static_library("user_prefs_tracked_test_support") {
   testonly = true
@@ skipping 22 matching lines @@
 
   deps = [
     ":user_prefs_tracked",
     ":user_prefs_tracked_test_support",
     "//base:base",
     "//base/test:test_support",
     "//components/prefs:test_support",
     "//testing/gtest",
   ]
 }