Add a mechanism for collecting Rappor samples on a daily interval.

components/rappor/rappor_pref_names.cc

 // 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.
 
 #include "components/rappor/rappor_pref_names.h"
 
 namespace rappor {
 namespace prefs {
 
 // Deprecated: Old cohort selection pref, should be cleared.
 const char kRapporCohortDeprecated[] = "rappor.cohort";
 
 // A randomly generated number, which determines cohorts data is reported for.
 const char kRapporCohortSeed[] = "rappor.cohort_seed";
 
+// Timestamp of the last time we sampled daily metrics.
+const char kRapporLastDailySample[] = "rappor.last_daily_sample";
+
 // A base-64 encoded, randomly generated byte string, which is used as a seed
 // for redacting collected data.
 // Important: This value should remain secret at the client, and never be
 // reported on the network, or to the server.
 const char kRapporSecret[] = "rappor.secret";
 
 }  // namespace prefs
 }  // namespace rappor