Enable startup tracing from command line flags in components/tracing

components/tracing/browser/trace_config_file.h

-// 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_BROWSER_TRACE_CONFIG_FILE_H_
-#define COMPONENTS_TRACING_BROWSER_TRACE_CONFIG_FILE_H_
-
-#include "base/files/file_path.h"
-#include "base/macros.h"
-#include "base/trace_event/trace_config.h"
-#include "build/build_config.h"
-#include "components/tracing/tracing_export.h"
-
-namespace base {
-template <typename Type> struct DefaultSingletonTraits;
-}  // namespace base
-
-namespace tracing {
-
-// TraceConfigFile is a singleton that contains the configurations of tracing.
-// One can create a trace config file and use it to configure startup and/or
-// shutdown tracing.
-//
-// The trace config file should be JSON formated. One example is:
-//   {
-//     "trace_config": {
-//        "record_mode": "record-until-full",
-//        "included_categories": ["cc", "skia"]
-//      },
-//      "startup_duration": 5,
-//      "result_file": "chrometrace.log"
-//   }
-//
-// trace_config:     The configuration of tracing. Please see the details in
-//                   base/trace_event/trace_config.h.
-//
-// startup_duration: The duration for startup tracing in terms of seconds.
-//                   Tracing will stop automatically after the duration. If this
-//                   value is not specified, the duration is 0 and one needs
-//                   to stop tracing by other ways, e.g., by DevTools, or get
-//                   the result file after shutting the browser down.
-//
-// result_file:      The file that contains the trace log. The default result
-//                   file path is chrometrace.log. Chrome will dump the trace
-//                   log to this file
-//                   1) after startup_duration if it is specified;
-//                   2) or after browser shutdown if startup duration is 0.
-//                   One can also stop tracing and get the result by other ways,
-//                   e.g., by DevTools. In that case, the trace log will not be
-//                   saved to this file.
-//                   Notice: This is not supported on Android. The result file
-//                   path will be generated by tracing controller.
-//
-// The trace config file can be specified by the --trace-config-file flag on
-// most platforms except on Android, e.g., --trace-config-file=path/to/file/.
-// This flag should not be used with --trace-startup or --trace-shutdown. If
-// those two flags are used, --trace-config-file flag will be ignored. If the
-// --trace-config-file flag is used without the file path, Chrome will do
-// startup tracing with 5 seconds' startup duration.
-//
-// On Android, Chrome does not read the --trace-config-file flag, because not
-// all Chrome based browsers read customized flag, e.g., Android WebView. Chrome
-// on Android reads from a fixed file location:
-//   /data/local/chrome-trace-config.json
-// If this file exists, Chrome will start tracing according to the configuration
-// specified in the file, otherwise, Chrome will not start tracing.
-class TRACING_EXPORT TraceConfigFile {
- public:
-  static TraceConfigFile* GetInstance();
-
-  bool IsEnabled() const;
-  base::trace_event::TraceConfig GetTraceConfig() const;
-  int GetStartupDuration() const;
-#if !defined(OS_ANDROID)
-  base::FilePath GetResultFile() const;
-#endif
-
- private:
-  // This allows constructor and destructor to be private and usable only
-  // by the Singleton class.
-  friend struct base::DefaultSingletonTraits<TraceConfigFile>;
-  TraceConfigFile();
-  ~TraceConfigFile();
-
-  bool ParseTraceConfigFileContent(const std::string& content);
-
-  bool is_enabled_;
-  base::trace_event::TraceConfig trace_config_;
-  int startup_duration_;
-  base::FilePath result_file_;
-
-  DISALLOW_COPY_AND_ASSIGN(TraceConfigFile);
-};
-
-}  // namespace tracing
-
-#endif  // COMPONENTS_TRACING_BROWSER_TRACE_CONFIG_FILE_H_