Move prefs::kLastPolicyStatisticsUpdate to the policy component.

components/policy/core/common/policy_pref_names.h

+// Copyright 2013 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.
+
+#ifndef COMPONENTS_POLICY_CORE_COMMON_PREF_NAMES_H_
+#define COMPONENTS_POLICY_CORE_COMMON_PREF_NAMES_H_
+
+#include "components/policy/policy_export.h"
+
+namespace policy {
+namespace prefs {
+
+// Constants for the names of policy-related preferences.
+// TODO(dconnelly): remove POLICY_EXPORT once the statistics collector moves
+// to the policy component (crbug.com/271392).
+POLICY_EXPORT extern const char kLastPolicyStatisticsUpdate[];
+
+}  // prefs
+}  // namespace policy
+
+#endif  // COMPONENTS_POLICY_CORE_COMMON_PREF_NAMES_H_