Convert FieldTrialList to Accept a std::unique_ptr

ios/chrome/browser/ios_chrome_main_parts.mm

 // Copyright 2016 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 "ios/chrome/browser/ios_chrome_main_parts.h"
 
 #include "base/base_switches.h"
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 183 matching lines @@
 // This will be called after the command-line has been mutated by about:flags
 void IOSChromeMainParts::SetUpMetricsAndFieldTrials() {
   base::SetRecordActionTaskRunner(
       web::WebThread::GetTaskRunnerForThread(web::WebThread::UI));
 
   // Initialize FieldTrialList to support FieldTrials that use one-time
   // randomization.
   DCHECK(!field_trial_list_);
   field_trial_list_.reset(
       new base::FieldTrialList(application_context_->GetMetricsServicesManager()
-                                   ->CreateEntropyProvider()
-                                   .release()));
+                                   ->CreateEntropyProvider()));
 
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();
   // Ensure any field trials specified on the command line are initialized.
   // Also stop the metrics service so that we don't pollute UMA.
   if (command_line->HasSwitch(switches::kForceFieldTrials)) {
     // Create field trials without activating them, so that this behaves in a
     // consistent manner with field trials created from the server.
     bool result = base::FieldTrialList::CreateTrialsFromString(
         command_line->GetSwitchValueASCII(switches::kForceFieldTrials),
@@ skipping 46 matching lines @@
 
 void IOSChromeMainParts::StartMetricsRecording() {
   bool wifiOnly = local_state_->GetBoolean(prefs::kMetricsReportingWifiOnly);
   bool isConnectionCellular = net::NetworkChangeNotifier::IsConnectionCellular(
       net::NetworkChangeNotifier::GetConnectionType());
   bool mayUpload = !wifiOnly || !isConnectionCellular;
 
   application_context_->GetMetricsServicesManager()->UpdateUploadPermissions(
       mayUpload);
 }