Use SequencedWorkerPool for disk operations in TraceSubscriberStdio.

base/test/trace_event_analyzer_unittest.cc

Index: base/test/trace_event_analyzer_unittest.cc
diff --git a/base/test/trace_event_analyzer_unittest.cc b/base/test/trace_event_analyzer_unittest.cc
index ccce3f31f2d7022ad741ce83b367c3388ab94328..8ff611f2cb6520d2a66bbe53b9c86e3b4f0990c8 100644
--- a/base/test/trace_event_analyzer_unittest.cc
+++ b/base/test/trace_event_analyzer_unittest.cc
@@ -15,8 +15,7 @@ class TraceEventAnalyzerTest : public testing::Test {
  public:
   void ManualSetUp();
   void OnTraceDataCollected(
-      const scoped_refptr<base::debug::TraceLog::RefCountedString>&
-          json_events_str);
+      const scoped_refptr<base::RefCountedString>& json_events_str);
   void BeginTracing();
   void EndTracing();
 
@@ -36,9 +35,8 @@ void TraceEventAnalyzerTest::ManualSetUp() {
 }
 
 void TraceEventAnalyzerTest::OnTraceDataCollected(
-    const scoped_refptr<base::debug::TraceLog::RefCountedString>&
-        json_events_str) {
-  buffer_.AddFragment(json_events_str->data);
+    const scoped_refptr<base::RefCountedString>& json_events_str) {
+  buffer_.AddFragment(json_events_str->data());
 }
 
 void TraceEventAnalyzerTest::BeginTracing() {