Use FILE thread for disk operations in TraceSubscriberStdio

content/common/child_trace_message_filter.cc

Index: content/common/child_trace_message_filter.cc
===================================================================
--- content/common/child_trace_message_filter.cc	(revision 123084)
+++ content/common/child_trace_message_filter.cc	(working copy)
@@ -72,8 +72,7 @@
 }
 
 void ChildTraceMessageFilter::OnTraceDataCollected(
-    const scoped_refptr<base::debug::TraceLog::RefCountedString>&
-        events_str_ptr) {
+    const scoped_refptr<base::RefCountedString>& events_str_ptr) {
   if (MessageLoop::current() != ChildProcess::current()->io_message_loop()) {
     ChildProcess::current()->io_message_loop()->PostTask(FROM_HERE,
         base::Bind(&ChildTraceMessageFilter::OnTraceDataCollected, this,
@@ -82,7 +81,7 @@
   }
 
   channel_->Send(new ChildProcessHostMsg_TraceDataCollected(
-    events_str_ptr->data));
+    events_str_ptr->data()));
 }
 
 void ChildTraceMessageFilter::OnTraceBufferFull() {