Revert of Delete base/prefs and update callers to use components.

ios/chrome/browser/metrics/ios_chrome_metrics_service_accessor.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 "ios/chrome/browser/metrics/ios_chrome_metrics_service_accessor.h"
 
 #include <stdint.h>
 
-#include "components/prefs/pref_service.h"
+#include "base/prefs/pref_service.h"
 #include "ios/chrome/browser/application_context.h"
 
 // static
 bool IOSChromeMetricsServiceAccessor::IsMetricsAndCrashReportingEnabled() {
   return IsMetricsReportingEnabled(GetApplicationContext()->GetLocalState());
 }
 
 // static
 bool IOSChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
     const std::string& trial_name,
     const std::string& group_name) {
   return metrics::MetricsServiceAccessor::RegisterSyntheticFieldTrial(
       GetApplicationContext()->GetMetricsService(), trial_name, group_name);
 }
 
 // static
 bool IOSChromeMetricsServiceAccessor::RegisterSyntheticFieldTrialWithNameHash(
     uint32_t trial_name_hash,
     const std::string& group_name) {
   return metrics::MetricsServiceAccessor::
       RegisterSyntheticFieldTrialWithNameHash(
           GetApplicationContext()->GetMetricsService(), trial_name_hash,
           group_name);
 }