Reland again [Startup Tracing] Add --trace-config-file flag

components/tracing/tracing_switches.cc

 // Copyright 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.
 
 #include "components/tracing/tracing_switches.h"
 
 namespace switches {
 
+// Causes TRACE_EVENT flags to be recorded from startup.
+// This flag will be ignored if --trace-startup or --trace-shutdown is provided.
+const char kTraceConfigFile[]               = "trace-config-file";
+
 // Causes TRACE_EVENT flags to be recorded beginning with shutdown. Optionally,
 // can specify the specific trace categories to include (e.g.
 // --trace-shutdown=base,net) otherwise, all events are recorded.
 // --trace-shutdown-file can be used to control where the trace log gets stored
 // to since there is otherwise no way to access the result.
 const char kTraceShutdown[]                 = "trace-shutdown";
 
 // If supplied, sets the file which shutdown tracing will be stored into, if
 // omitted the default will be used "chrometrace.log" in the current directory.
 // Has no effect unless --trace-shutdown is also supplied.
@@ skipping 20 matching lines @@
 // Example: --trace-startup --trace-startup-file=/tmp/trace_event.log
 // As a special case, can be set to 'none' - this disables automatically saving
 // the result to a file and the first manually recorded trace will then receive
 // all events since startup.
 const char kTraceStartupFile[]              = "trace-startup-file";
 
 // Sets the target URL for uploading tracing data.
 const char kTraceUploadURL[]                = "trace-upload-url";
 
 }  // namespace switches