[Startup Tracing] Enable startup tracing from config file

components/tracing/startup_tracing.h

Index: components/tracing/startup_tracing.h
diff --git a/components/tracing/startup_tracing.h b/components/tracing/startup_tracing.h
new file mode 100644
index 0000000000000000000000000000000000000000..ae68f6fa654e17736c7ffef9126a2aa8d2ab9911
--- /dev/null
+++ b/components/tracing/startup_tracing.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2015 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 COMPONENTS_TRACING_STARTUP_TRACING_H_
+#define COMPONENTS_TRACING_STARTUP_TRACING_H_
+
+namespace tracing {
+
+// Enable startup tracing according to the trace config file. If the trace
+// config file does not exist, it will do nothing. This is designed to be used
+// by Telemetry. Telemetry will stop tracing via DevTools later. To avoid
+// conflict, this should not be used when --trace-startup is enabled.
+void EnableStartupTracingIfConfigFileExists();
+
+}  // namespace tracing
+
+#endif  // COMPONENTS_TRACING_STARTUP_TRACING_H_