Make MediaFileUtil run on thread pool.

webkit/fileapi/file_system_operation_context.cc

Index: webkit/fileapi/file_system_operation_context.cc
diff --git a/webkit/fileapi/file_system_operation_context.cc b/webkit/fileapi/file_system_operation_context.cc
index 196e3b8380bbab97db7bbf9eb2d73c290b7ef970..f29a78744b85ac027946e14b27cd3dbee6b20527 100644
--- a/webkit/fileapi/file_system_operation_context.cc
+++ b/webkit/fileapi/file_system_operation_context.cc
@@ -4,6 +4,7 @@
 
 #include "webkit/fileapi/file_system_operation_context.h"
 
+#include "base/sequenced_task_runner.h"
 #include "webkit/fileapi/file_system_context.h"
 
 namespace fileapi {
@@ -11,13 +12,14 @@ namespace fileapi {
 FileSystemOperationContext::FileSystemOperationContext(
     FileSystemContext* context)
     : file_system_context_(context),
+      task_runner_(file_system_context_->file_task_runner()),
       allowed_bytes_growth_(0) {}
 
 FileSystemOperationContext::~FileSystemOperationContext() {}
 
-base::SequencedTaskRunner*
-FileSystemOperationContext::file_task_runner() const {
-  return file_system_context_->file_task_runner();
+void FileSystemOperationContext::SetTaskRunner(
+    base::SequencedTaskRunner* task_runner) {
+  task_runner_ = task_runner;
 }
 
 }  // namespace fileapi