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

services/asset_bundle/asset_unpacker_job.h

Index: services/asset_bundle/asset_unpacker_job.h
diff --git a/services/asset_bundle/asset_unpacker_job.h b/services/asset_bundle/asset_unpacker_job.h
index 06759718700908e0284234ca004d39587710176e..66c2b331e84d2a04599258716bd53cc8f31e4222 100644
--- a/services/asset_bundle/asset_unpacker_job.h
+++ b/services/asset_bundle/asset_unpacker_job.h
@@ -8,6 +8,7 @@
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/task_runner.h"
 #include "mojo/common/data_pipe_utils.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/services/asset_bundle/public/interfaces/asset_bundle.mojom.h"
@@ -17,7 +18,8 @@ namespace asset_bundle {
 
 class AssetUnpackerJob {
  public:
-  AssetUnpackerJob(InterfaceRequest<AssetBundle> asset_bundle);
+  AssetUnpackerJob(InterfaceRequest<AssetBundle> asset_bundle,
+                   scoped_refptr<base::TaskRunner> worker_runner);
   ~AssetUnpackerJob();
 
   void Unpack(ScopedDataPipeConsumerHandle zipped_assets);
@@ -27,6 +29,7 @@ class AssetUnpackerJob {
   void OnUnzippedAssetsAvailable(scoped_ptr<base::ScopedTempDir> temp_dir);
 
   InterfaceRequest<AssetBundle> asset_bundle_;
+  scoped_refptr<base::TaskRunner> worker_runner_;
   base::WeakPtrFactory<AssetUnpackerJob> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AssetUnpackerJob);