Clear client id prefs when opting out of UMA.

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 <stddef.h>
 
 #include "base/command_line.h"
 #include "base/guid.h"
@@ skipping 65 matching lines @@
 MetricsStateManager::~MetricsStateManager() {
   DCHECK(instance_exists_);
   instance_exists_ = false;
 }
 
 bool MetricsStateManager::IsMetricsReportingEnabled() {
   return enabled_state_provider_->IsReportingEnabled();
 }
 
 void MetricsStateManager::ForceClientIdCreation() {
-  if (!client_id_.empty())
-    return;
+  {
+    std::string client_id_from_prefs =
+        local_state_->GetString(prefs::kMetricsClientID);
+    // If client id in prefs matches the cached copy, return early.
+    if (!client_id_from_prefs.empty() && client_id_from_prefs == client_id_)
+      return;
+    client_id_.swap(client_id_from_prefs);
+  }
 
-  client_id_ = local_state_->GetString(prefs::kMetricsClientID);
   if (!client_id_.empty()) {
     // It is technically sufficient to only save a backup of the client id when
     // it is initially generated below, but since the backup was only introduced
     // in M38, seed it explicitly from here for some time.
     BackUpCurrentClientInfo();
     return;
   }
 
   const std::unique_ptr<ClientInfo> client_info_backup =
       LoadClientInfoAndMaybeMigrate();
@@ skipping 221 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