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

content/browser/tracing/add_new_file_index.cc

Index: content/browser/tracing/add_new_file_index.cc
diff --git a/content/browser/tracing/add_new_file_index.cc b/content/browser/tracing/add_new_file_index.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a41edbc0bef3b8fc29eacd9a05690b548a28a579
--- /dev/null
+++ b/content/browser/tracing/add_new_file_index.cc
@@ -0,0 +1,27 @@
+// 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.
+
+#include "content/browser/tracing/add_new_file_index.h"
+
+#include "base/file_util.h"
+#include "base/strings/string_number_conversions.h"
+
+namespace {
+const unsigned int kMaxLogFileIndex = 1000000;
+}
+
+namespace content {
+
+base::FilePath AddNewLogFileIndex(const base::FilePath& trace_file) {
+  // trace file should be initialized synchronously
+  for (unsigned int i = 0; i < kMaxLogFileIndex; ++i) {
+    const base::FilePath new_filename(
+        trace_file.AppendASCII("." + base::UintToString(i)));
+    if (!base::PathExists(new_filename))
+      return new_filename;
+  }
+  return trace_file;
+}
+
+}  // namespace content