Eliminate content::BrowserThread knowledge from VariationsService

chrome/browser/metrics/variations/chrome_variations_service_client.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 "chrome/browser/metrics/variations/chrome_variations_service_client.h"
 
 #include "chrome/browser/browser_process.h"
+#include "content/public/browser/browser_thread.h"
 
 ChromeVariationsServiceClient::ChromeVariationsServiceClient() {}
 
 ChromeVariationsServiceClient::~ChromeVariationsServiceClient() {}
 
 std::string ChromeVariationsServiceClient::GetApplicationLocale() {
   return g_browser_process->GetApplicationLocale();
 }
 
+base::SequencedWorkerPool* ChromeVariationsServiceClient::GetBlockingPool() {
+  return content::BrowserThread::GetBlockingPool();
+}
+
 net::URLRequestContextGetter*
 ChromeVariationsServiceClient::GetURLRequestContext() {
   return g_browser_process->system_request_context();
 }
 
 network_time::NetworkTimeTracker*
 ChromeVariationsServiceClient::GetNetworkTimeTracker() {
   return g_browser_process->network_time_tracker();
 }
 
 void ChromeVariationsServiceClient::OnInitialStartup() {
 #if defined(OS_WIN)
   StartGoogleUpdateRegistrySync();
 #endif
 }
 
 #if defined(OS_WIN)
 void ChromeVariationsServiceClient::StartGoogleUpdateRegistrySync() {
   registry_syncer_.RequestRegistrySync();
 }
 #endif