Use FILE thread for disk operations in TraceSubscriberStdio

base/debug/trace_event_unittest.cc

Index: base/debug/trace_event_unittest.cc
===================================================================
--- base/debug/trace_event_unittest.cc	(revision 123084)
+++ base/debug/trace_event_unittest.cc	(working copy)
@@ -42,7 +42,7 @@
   // up multiple times when testing AtExit. Use ManualTestSetUp for this.
   void ManualTestSetUp();
   void OnTraceDataCollected(
-      const scoped_refptr<TraceLog::RefCountedString>& events_str);
+      const scoped_refptr<base::RefCountedString>& events_str);
   DictionaryValue* FindMatchingTraceEntry(const JsonKeyValue* key_values);
   DictionaryValue* FindNamePhase(const char* name, const char* phase);
   DictionaryValue* FindNamePhaseKeyValue(const char* name,
@@ -91,11 +91,11 @@
 }
 
 void TraceEventTestFixture::OnTraceDataCollected(
-    const scoped_refptr<TraceLog::RefCountedString>& events_str) {
+    const scoped_refptr<base::RefCountedString>& events_str) {
   AutoLock lock(lock_);
   json_output_.json_output.clear();
   trace_buffer_.Start();
-  trace_buffer_.AddFragment(events_str->data);
+  trace_buffer_.AddFragment(events_str->data());
   trace_buffer_.Finish();
 
   scoped_ptr<Value> root;