Add --trace-rotate-startup-file option and store unsaved trace data on exit.

content/browser/tracing/add_new_file_index.h

+// Copyright 2014 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.
+
+#ifndef CONTENT_BROWSER_TRACING_ADD_NEW_FILE_INDEX_H_
+#define CONTENT_BROWSER_TRACING_ADD_NEW_FILE_INDEX_H_
+
+namespace base {
+class FilePath;
+}
+
+namespace content {
+
+// Add first unused number file suffix ".0", ".1", ... up to kMaxLogFileIndex.
+// Returns |trace_file| if all indexes are used.
+// Note, that it should be synchronous to delay UI thread before log
+// file name is selected. Therefore it is called before threads are set up.
+base::FilePath AddNewLogFileIndex(const base::FilePath& trace_file);
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_TRACING_ADD_NEW_FILE_INDEX_H_