Make MediaFileUtil run on thread pool.

content/browser/fileapi/browser_file_system_helper.cc

Index: content/browser/fileapi/browser_file_system_helper.cc
diff --git a/content/browser/fileapi/browser_file_system_helper.cc b/content/browser/fileapi/browser_file_system_helper.cc
index a6321b04b4a440e5e4b1088a92821efb49052b6b..ed67f7651a7114532f1c10f73bd20f70ec111e6d 100644
--- a/content/browser/fileapi/browser_file_system_helper.cc
+++ b/content/browser/fileapi/browser_file_system_helper.cc
@@ -9,6 +9,7 @@
 
 #include "base/command_line.h"
 #include "base/file_path.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_switches.h"
 #include "webkit/fileapi/file_system_options.h"
@@ -43,7 +44,12 @@ scoped_refptr<fileapi::FileSystemContext> CreateFileSystemContext(
         const FilePath& profile_path, bool is_incognito,
         quota::SpecialStoragePolicy* special_storage_policy,
         quota::QuotaManagerProxy* quota_manager_proxy) {
+  base::SequencedWorkerPool* pool = BrowserThread::GetBlockingPool();
+  base::SequencedWorkerPool::SequenceToken media_sequence_token =
+      pool->GetSequenceToken();
+
   return new fileapi::FileSystemContext(
+      pool->GetSequencedTaskRunner(media_sequence_token),
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE),
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO),
       special_storage_policy,