Eliminate content::BrowserThread knowledge from VariationsService

components/variations/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 COMPONENTS_VARIATIONS_VARIATIONS_SERVICE_CLIENT_H_
 #define COMPONENTS_VARIATIONS_VARIATIONS_SERVICE_CLIENT_H_
 
 #include <string>
 
+namespace base {
+class SequencedWorkerPool;
+}
+
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace network_time {
 class NetworkTimeTracker;
 }
 
 namespace chrome_variations {
 
 // An abstraction of operations that depend on the embedder's (e.g. Chrome)
 // environment.
 class VariationsServiceClient {
  public:
   virtual ~VariationsServiceClient() {}
 
   // Returns the current application locale (e.g. "en-US").
   virtual std::string GetApplicationLocale() = 0;
 
+  // Returns the SequencedWorkerPool on which the VariationsService should run
+  // tasks that may block.
+  virtual base::SequencedWorkerPool* GetBlockingPool() = 0;
+
   virtual net::URLRequestContextGetter* GetURLRequestContext() = 0;
   virtual network_time::NetworkTimeTracker* GetNetworkTimeTracker() = 0;
 
   // Called from VariationsService::PerformPreMainMessageLoopStartup().
   virtual void OnInitialStartup() {}
 };
 
 }  // namespace chrome_variations
 
 #endif  // COMPONENTS_VARIATIONS_VARIATIONS_SERVICE_CLIENT_H_