gdata: Fix a bug that blocked FILE thread when loading large feeds.

chrome/browser/chromeos/gdata/gdata_file_system.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/chromeos/gdata/gdata_file_system.h"
 
 #include <errno.h>
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/eintr_wrapper.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
 #include "base/platform_file.h"
 #include "base/threading/platform_thread.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/gdata/gdata_documents_service.h"
 #include "chrome/browser/chromeos/gdata/gdata_download_observer.h"
 #include "chrome/browser/chromeos/gdata/gdata_sync_client.h"
 #include "chrome/browser/chromeos/gdata/gdata_system_service.h"
 #include "chrome/browser/chromeos/gdata/gdata_upload_file_info.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths_internal.h"
@@ skipping 1790 matching lines @@
 }
 
 void GDataFileSystem::LoadRootFeedFromCache(
     const FilePath& search_file_path,
     bool should_load_from_server,
     const FindFileCallback& callback) {
   base::PlatformFileError* error =
       new base::PlatformFileError(base::PLATFORM_FILE_OK);
   base::ListValue* feed_list = new base::ListValue;
 
-  PostBlockingPoolSequencedTaskAndReply(
-      kGDataFileSystemToken,
+  // Post a task without the sequence token, as this doesn't have to be
+  // sequenced with other tasks, and can take long if the feed is large.
+  // Note that it's OK to do this before the cache is initialized.
+  BrowserThread::GetBlockingPool()->PostTaskAndReply(
       FROM_HERE,
       base::Bind(&GDataFileSystem::LoadRootFeedOnIOThreadPool,
                  cache_paths_[GDataRootDirectory::CACHE_TYPE_META].Append(
                      kLastFeedFile),
                  error,
                  feed_list),
       base::Bind(&GDataFileSystem::OnLoadRootFeed,
                  GetWeakPtrForCurrentThread(),
                  search_file_path,
                  should_load_from_server,
@@ skipping 1787 matching lines @@
       BrowserThread::FILE,
       from_here,
       base::Bind(&GDataFileSystem::RunTaskOnIOThreadPool,
                  base::Unretained(this),
                  request_task),
       reply_task);
   DCHECK(posted);
 }
 
 }  // namespace gdata