Add function to register a synthetic trial with the trial hash.

chrome/browser/metrics/metrics_service_accessor.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 "chrome/browser/metrics/metrics_service_accessor.h"
 
 #include "chrome/browser/browser_process.h"
 #include "components/metrics/metrics_service.h"
 #include "components/metrics/metrics_service_observer.h"
-#include "components/variations/metrics_util.h"
 
 // static
 void MetricsServiceAccessor::AddMetricsServiceObserver(
     MetricsServiceObserver* observer) {
   MetricsService* metrics_service = g_browser_process->metrics_service();
   if (metrics_service)
     metrics_service->AddObserver(observer);
 }
 
 void MetricsServiceAccessor::RemoveMetricsServiceObserver(
     MetricsServiceObserver* observer) {
   MetricsService* metrics_service = g_browser_process->metrics_service();
   if (metrics_service)
     metrics_service->RemoveObserver(observer);
 }
 
 // static
 bool MetricsServiceAccessor::RegisterSyntheticFieldTrial(
     MetricsService* metrics_service,
-    const std::string& trial,
-    const std::string& group) {
+    uint32_t trial_name_hash,
+    uint32_t group_name_hash) {
   if (!metrics_service)
     return false;
 
-  SyntheticTrialGroup trial_group(metrics::HashName(trial),
-                                  metrics::HashName(group));
+  SyntheticTrialGroup trial_group(trial_name_hash, group_name_hash);
   metrics_service->RegisterSyntheticFieldTrial(trial_group);
   return true;
 }