Use SequencedWorkerPool for disk operations in TraceSubscriberStdio.

chrome/browser/automation/automation_provider.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/automation/automation_provider.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 388 matching lines @@
 void AutomationProvider::OnEndTracingComplete() {
   IPC::Message* reply_message = tracing_data_.reply_message.release();
   if (reply_message) {
     AutomationMsg_EndTracing::WriteReplyParams(
         reply_message, tracing_data_.trace_output.size(), true);
     Send(reply_message);
   }
 }
 
 void AutomationProvider::OnTraceDataCollected(
-    const std::string& trace_fragment) {
-  tracing_data_.trace_output.push_back(trace_fragment);
+    const scoped_refptr<base::RefCountedString>& trace_fragment) {
+  tracing_data_.trace_output.push_back(trace_fragment->data());
 }
 
 bool AutomationProvider::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   bool deserialize_success = true;
   IPC_BEGIN_MESSAGE_MAP_EX(AutomationProvider, message, deserialize_success)
 #if !defined(OS_MACOSX)
     IPC_MESSAGE_HANDLER_DELAY_REPLY(AutomationMsg_WindowDrag,
                                     WindowSimulateDrag)
 #endif  // !defined(OS_MACOSX)
@@ skipping 590 matching lines @@
     }
   }
 }
 
 void AutomationProvider::SaveAsAsync(int tab_handle) {
   NavigationController* tab = NULL;
   WebContents* web_contents = GetWebContentsForHandle(tab_handle, &tab);
   if (web_contents)
     web_contents->OnSavePage();
 }