Add a Rappor option in the settings page.

components/rappor/rappor_prefs.cc

 // Copyright 2015 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_prefs.h"
 
 #include "base/base64.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
@@ skipping 20 matching lines @@
 
 void RecordLoadSecretResult(LoadResult reason) {
   UMA_HISTOGRAM_ENUMERATION(kLoadSecretHistogramName,
                             reason,
                             NUM_LOAD_RESULTS);
 }
 
 } // namespace
 
 void RegisterPrefs(PrefRegistrySimple* registry) {
+  registry->RegisterBooleanPref(prefs::kRapporEnabled, true);
   registry->RegisterStringPref(prefs::kRapporSecret, std::string());
   registry->RegisterIntegerPref(prefs::kRapporCohortDeprecated, -1);
   registry->RegisterIntegerPref(prefs::kRapporCohortSeed, -1);
   metrics::DailyEvent::RegisterPref(registry, prefs::kRapporLastDailySample);
 }
 
 int32_t LoadCohort(PrefService* pref_service) {
   // Ignore and delete old cohort parameter.
   pref_service->ClearPref(prefs::kRapporCohortDeprecated);
 
@@ skipping 38 matching lines @@
   DVLOG(2) << "Generated a new Rappor secret.";
   secret = HmacByteVectorGenerator::GenerateEntropyInput();
   base::Base64Encode(secret, &secret_base64);
   pref_service->SetString(prefs::kRapporSecret, secret_base64);
   return secret;
 }
 
 }  // namespace internal
 
 }  // namespace rappor