[Blob] BlobReader class & tests, and removal of all redundant reading.

content/browser/loader/upload_data_stream_builder.h

 // Copyright 2013 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 CONTENT_BROWSER_LOADER_UPLOAD_DATA_STREAM_BUILDER_H_
 #define CONTENT_BROWSER_LOADER_UPLOAD_DATA_STREAM_BUILDER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
 
 namespace base {
-class TaskRunner;
+class SingleThreadTaskRunner;
 }
 
 namespace storage {
 class FileSystemContext;
 }
 
 namespace net {
 class UploadDataStream;
 }
 
@@ skipping 14 matching lines @@
   // by binding the BlobDataHandles of them to ResourceRequestBody in
   // ResourceDispatcherHostImpl::BeginRequest().
   //
   // |file_system_context| is used to create a FileStreamReader for files with
   // filesystem URLs.  |file_task_runner| is used to perform file operations
   // when the data gets uploaded.
   static scoped_ptr<net::UploadDataStream> Build(
       ResourceRequestBody* body,
       storage::BlobStorageContext* blob_context,
       storage::FileSystemContext* file_system_context,
-      base::TaskRunner* file_task_runner);
+      base::SingleThreadTaskRunner* file_task_runner);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_UPLOAD_DATA_STREAM_BUILDER_H_