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

components/tracing/trace_config_file.h

Index: components/tracing/trace_config_file.h
diff --git a/components/tracing/trace_config_file.h b/components/tracing/trace_config_file.h
new file mode 100644
index 0000000000000000000000000000000000000000..273f9f1c48a9f38b18424c00b5db0c236a57b098
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+++ b/components/tracing/trace_config_file.h
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+// 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_TRACE_CONFIG_FILE_H_
+#define COMPONENTS_TRACING_TRACE_CONFIG_FILE_H_
+
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "base/trace_event/trace_config.h"
+#include "components/tracing/tracing_export.h"
+
+template <typename Type> struct DefaultSingletonTraits;
+
+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 DefaultSingletonTraits<TraceConfigFile>;
+  TraceConfigFile();
+  ~TraceConfigFile();
+
+  bool ParseTraceConfigFileContent(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_TRACE_CONFIG_FILE_H_