Eliminate content::BrowserThread knowledge from VariationsService

chrome/browser/metrics/variations/chrome_variations_service_client.h

 // 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.
 
 #ifndef CHROME_BROWSER_METRICS_VARIATIONS_CHROME_VARIATIONS_SERVICE_CLIENT_H_
 #define CHROME_BROWSER_METRICS_VARIATIONS_CHROME_VARIATIONS_SERVICE_CLIENT_H_
 
 #include "base/basictypes.h"
 #include "components/variations/variations_service_client.h"
 
 #if defined(OS_WIN)
 #include "chrome/browser/metrics/variations/variations_registry_syncer_win.h"
 #endif
 
 // ChromeVariationsServiceClient provides an implementation of
 // VariationsServiceClient that depends on chrome/.
 class ChromeVariationsServiceClient
     : public chrome_variations::VariationsServiceClient {
  public:
   ChromeVariationsServiceClient();
   ~ChromeVariationsServiceClient() override;
 
   // chrome_variations::VariationsServiceClient:
   std::string GetApplicationLocale() override;
+  base::SequencedWorkerPool* GetBlockingPool() override;
   net::URLRequestContextGetter* GetURLRequestContext() override;
   network_time::NetworkTimeTracker* GetNetworkTimeTracker() override;
   void OnInitialStartup() override;
 
  private:
 #if defined(OS_WIN)
   // Starts syncing Google Update Variation IDs with the registry.
   void StartGoogleUpdateRegistrySync();
 
   // Helper that handles synchronizing Variations with the Registry.
   chrome_variations::VariationsRegistrySyncer registry_syncer_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ChromeVariationsServiceClient);
 };
 
 #endif  // CHROME_BROWSER_METRICS_VARIATIONS_CHROME_VARIATIONS_SERVICE_CLIENT_H_