Use SequencedWorkerPool for disk operations in TraceSubscriberStdio.

content/common/child_trace_message_filter.cc

Index: content/common/child_trace_message_filter.cc
diff --git a/content/common/child_trace_message_filter.cc b/content/common/child_trace_message_filter.cc
index ca280bc8c417f7ff8516ab1d0e09d2910b4f9bef..9259ac07629f339620b5e95d1d2cef8142a1eba5 100644
--- a/content/common/child_trace_message_filter.cc
+++ b/content/common/child_trace_message_filter.cc
@@ -72,8 +72,7 @@ void ChildTraceMessageFilter::OnGetTraceBufferPercentFull() {
 }
 
 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 @@ void ChildTraceMessageFilter::OnTraceDataCollected(
   }
 
   channel_->Send(new ChildProcessHostMsg_TraceDataCollected(
-    events_str_ptr->data));
+    events_str_ptr->data()));
 }
 
 void ChildTraceMessageFilter::OnTraceBufferFull() {