Move tracked prefs into services/preferences/tracked.

services/preferences/public/cpp/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("tracked") {
+  sources = [
+    "configuration.cc",
+    "configuration.h",
+    "pref_names.cc",
+    "pref_names.h",
+    "tracked_preference_histogram_names.cc",
+    "tracked_preference_histogram_names.h",
+  ]
+  public_deps = [
+    "//services/preferences/public/interfaces",
+  ]
+  deps = [
+    "//base",
+  ]
+}
+
+static_library("test_support") {
+  testonly = true
+  sources = [
+    "mock_validation_delegate.cc",
+    "mock_validation_delegate.h",
+  ]
+
+  deps = [
+    "//base",
+    "//services/preferences/public/interfaces",
+  ]
+}