Delete code corresponding to old UMA prefs.

components/metrics/metrics_state_manager.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/metrics/metrics_state_manager.h"
 
 #include "base/command_line.h"
 #include "base/guid.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
@@ skipping 106 matching lines @@
     // Flush the backup back to persistent storage in case we re-generated
     // missing data above.
     BackUpCurrentClientInfo();
     return;
   }
 
   // Failing attempts at getting an existing client ID, generate a new one.
   client_id_ = base::GenerateGUID();
   local_state_->SetString(prefs::kMetricsClientID, client_id_);
 
   if (local_state_->GetString(prefs::kMetricsOldClientID).empty()) {

[jwd, 2015/05/29 18:46:22]

What about this migration code, and obsoleting the related histograms?

[Alexei Svitkine (slow), 2015/05/29 18:59:17]

Err, you're right. Done.

     // Record the timestamp of when the user opted in to UMA.
     local_state_->SetInt64(prefs::kMetricsReportingEnabledTimestamp,
                            base::Time::Now().ToTimeT());
   } else {
     UMA_HISTOGRAM_BOOLEAN("UMA.ClientIdMigrated", true);
   }
   local_state_->ClearPref(prefs::kMetricsOldClientID);
 
   BackUpCurrentClientInfo();
 }
@@ skipping 63 matching lines @@
 // static
 void MetricsStateManager::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterBooleanPref(prefs::kMetricsResetIds, false);
   registry->RegisterStringPref(prefs::kMetricsClientID, std::string());
   registry->RegisterInt64Pref(prefs::kMetricsReportingEnabledTimestamp, 0);
   registry->RegisterIntegerPref(prefs::kMetricsLowEntropySource,
                                 kLowEntropySourceNotSet);
 
   ClonedInstallDetector::RegisterPrefs(registry);
   CachingPermutedEntropyProvider::RegisterPrefs(registry);
-
-  // TODO(asvitkine): Remove these once a couple of releases have passed.
-  // http://crbug.com/357704
-  registry->RegisterStringPref(prefs::kMetricsOldClientID, std::string());
-  registry->RegisterIntegerPref(prefs::kMetricsOldLowEntropySource, 0);
 }
 
 void MetricsStateManager::BackUpCurrentClientInfo() {
   ClientInfo client_info;
   client_info.client_id = client_id_;
   client_info.installation_date = local_state_->GetInt64(prefs::kInstallDate);
   client_info.reporting_enabled_date =
       local_state_->GetInt64(prefs::kMetricsReportingEnabledTimestamp);
   store_client_info_.Run(client_info);
 }
@@ skipping 84 matching lines @@
 
   local_state_->ClearPref(prefs::kMetricsClientID);
   local_state_->ClearPref(prefs::kMetricsLowEntropySource);
   local_state_->ClearPref(prefs::kMetricsResetIds);
 
   // Also clear the backed up client info.
   store_client_info_.Run(ClientInfo());
 }
 
 }  // namespace metrics