Make MediaFileUtil run on thread pool.

webkit/fileapi/file_system_context.cc

Index: webkit/fileapi/file_system_context.cc
diff --git a/webkit/fileapi/file_system_context.cc b/webkit/fileapi/file_system_context.cc
index 53afbb1248ccfa2ac22847dec174743dc6c9e29c..4b9aae41b2c6fc61a9f40848de44d843df0df287 100644
--- a/webkit/fileapi/file_system_context.cc
+++ b/webkit/fileapi/file_system_context.cc
@@ -46,6 +46,7 @@ void DidOpenFileSystem(FileSystemContext::OpenFileSystemCallback callback,
 }  // anonymous namespace
 
 FileSystemContext::FileSystemContext(
+    base::SequencedTaskRunner* media_task_runner,
     base::SequencedTaskRunner* file_task_runner,
     base::SingleThreadTaskRunner* io_task_runner,
     quota::SpecialStoragePolicy* special_storage_policy,
@@ -60,7 +61,7 @@ FileSystemContext::FileSystemContext(
               file_task_runner,
               profile_path,
               options)),
-      isolated_provider_(new IsolatedMountPointProvider) {
+      isolated_provider_(new IsolatedMountPointProvider(media_task_runner)) {
   if (quota_manager_proxy) {
     quota_manager_proxy->RegisterClient(CreateQuotaClient(
             this, options.is_incognito()));