Tracing: fix missing comma between trace chunks written to file

content/browser/tracing/tracing_controller_impl.cc

 // Copyright (c) 2013 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 "content/browser/tracing/tracing_controller_impl.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/files/file_util.h"
 #include "base/json/string_escape.h"
 #include "base/macros.h"
@@ skipping 50 matching lines @@
         BrowserThread::FILE,
         FROM_HERE,
         base::Bind(&FileTraceDataSink::CloseOnFileThread, this));
   }
 
  private:
   virtual ~FileTraceDataSink() { DCHECK(file_ == NULL); }
 
   void AddTraceChunkOnFileThread(
       const scoped_refptr<base::RefCountedString> chunk) {
-    if (!OpenFileIfNeededOnFileThread())
+    if (file_ != NULL)
+      fputc(',', file_);
+    else if (!OpenFileIfNeededOnFileThread())
       return;
     ignore_result(fwrite(chunk->data().c_str(), strlen(chunk->data().c_str()),
         1, file_));
   }
 
   bool OpenFileIfNeededOnFileThread() {
     if (file_ != NULL)
       return true;
     file_ = base::OpenFile(file_path_, "w");
     if (file_ == NULL) {
@@ skipping 793 matching lines @@
   is_monitoring_ = is_monitoring;
 #if !defined(OS_ANDROID)
   for (std::set<TracingUI*>::iterator it = tracing_uis_.begin();
        it != tracing_uis_.end(); it++) {
     (*it)->OnMonitoringStateChanged(is_monitoring);
   }
 #endif
 }
 
 }  // namespace content