Enable startup tracing from command line flags in components/tracing

components/tracing/common/trace_startup.h

+// Copyright 2017 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_COMMON_TRACE_STARTUP_H
+#define COMPONENTS_TRACING_COMMON_TRACE_STARTUP_H
+
+#include "base/command_line.h"
+#include "components/tracing/tracing_export.h"
+
+namespace tracing {
+
+// Enables TraceLog with config based on the command line flags passed. If
+// |can_access_file_system| is false then TraceLog is not enabled in case it is
+// required to read config file to start tracing.
+void TRACING_EXPORT
+EnableStartupTracingIfNeeded(const base::CommandLine& command_line,

[Primiano Tucci (use gerrit), 2017/02/15 15:33:34]

There doesn't seem to be an actual need of passing the command_line. It seems
you can just do CommandLine::ForCurrentProcess in the .cc file. there doesn't
seem to be any precedent for passing the cmdline around.

[ssid, 2017/02/15 18:35:34]

Done.

+                             bool can_access_file_system);
+
+}  // namespace tracing
+
+#endif  // COMPONENTS_TRACING_COMMON_TRACE_STARTUP_H