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),

[kinuko, 2012/08/02 21:12:46]

Having this as the first argument makes me feel that this task runner is the
most important TR while it would not.

[tzik, 2012/08/03 22:29:18]

Done.

       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE),
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO),

[kinuko, 2012/08/02 21:12:46]

When we have more and more task runners this wouldn't scale well.  It could be
in a different CL but maybe we could have a separate class which returns
appropriate task runners for different purposes (Media/File/IO/etc)?
Some FileUtil/FileSystemOperation might need to handle multiple task runners and
would be nice to have some neat interface.
Mock implementation of the class just return current message loop.  Chrome
implementation could keep multiple sequence tokens and return appropriate TRs.

[tzik, 2012/08/03 22:29:18]

Done.

       special_storage_policy,