Don't use base::WorkerPool in the asset_bundle app.

services/asset_bundle/asset_unpacker_impl.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 SERVICES_ASSET_BUNDLE_ASSET_UNPACKER_IMPL_H_
 #define SERVICES_ASSET_BUNDLE_ASSET_UNPACKER_IMPL_H_
 
 #include "base/macros.h"
+#include "base/task_runner.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "mojo/public/cpp/system/data_pipe.h"
 #include "mojo/services/asset_bundle/public/interfaces/asset_bundle.mojom.h"
 
 namespace mojo {
 namespace asset_bundle {
 
 class AssetUnpackerImpl : public AssetUnpacker {
  public:
-  AssetUnpackerImpl(InterfaceRequest<AssetUnpacker> request);
+  AssetUnpackerImpl(InterfaceRequest<AssetUnpacker> request,
+                    scoped_refptr<base::TaskRunner> worker_runner);
   ~AssetUnpackerImpl() override;
 
   // AssetUnpacker implementation
   void UnpackZipStream(ScopedDataPipeConsumerHandle zipped_assets,
                        InterfaceRequest<AssetBundle> asset_bundle) override;
 
  private:
   StrongBinding<AssetUnpacker> binding_;
 
+  scoped_refptr<base::TaskRunner> worker_runner_;
+
   DISALLOW_COPY_AND_ASSIGN(AssetUnpackerImpl);
 };
 
 }  // namespace asset_bundle
 }  // namespace mojo
 
 #endif  // SERVICES_ASSET_BUNDLE_ASSET_UNPACKER_IMPL_H_