Add a file thread to the renderer process.

chrome/renderer/render_thread.cc

Index: chrome/renderer/render_thread.cc
===================================================================
--- chrome/renderer/render_thread.cc	(revision 56828)
+++ chrome/renderer/render_thread.cc	(working copy)
@@ -307,6 +307,10 @@
   db_message_filter_ = NULL;
   RemoveFilter(devtools_agent_filter_.get());
 
+  // Shutdown the file thread if it's running.
+  if (file_thread_.get())
+    file_thread_->Stop();
+
   if (webkit_client_.get())
     WebKit::shutdown();
 
@@ -1100,3 +1104,13 @@
 
   return std::string();
 }
+
+scoped_refptr<base::MessageLoopProxy>
+RenderThread::GetFileThreadMessageLoopProxy() {
+  DCHECK(message_loop() == MessageLoop::current());
+  if (!file_thread_.get()) {
+    file_thread_.reset(new base::Thread("Renderer::FILE"));
+    file_thread_->Start();
+  }
+  return file_thread_->message_loop_proxy();
+}