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

components/tracing/startup_tracing.cc

-// 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.
-
-#include "components/tracing/startup_tracing.h"
-
-#include "base/files/file_path.h"
-#include "base/files/file_util.h"
-#include "base/path_service.h"
-#include "base/trace_event/trace_event.h"
-
-namespace tracing {
-
-namespace {
-
-// Maximum trace config file size that will be loaded, in bytes.
-const size_t kTraceConfigFileSizeLimit = 64 * 1024;
-
-// Trace config file path:
-// - Android: /data/local/.config/chrome-trace-config.json
-// - POSIX other than Android: $HOME/.config/chrome-trace-config.json
-// - Win: %USERPROFILE%/.config/chrome-trace-config.json
-#if defined(OS_ANDROID)
-const base::FilePath::CharType kAndroidTraceConfigDir[] =
-    FILE_PATH_LITERAL("/data/local");
-#endif
-
-const base::FilePath::CharType kChromeConfigDir[] =
-    FILE_PATH_LITERAL(".config");
-const base::FilePath::CharType kTraceConfigFileName[] =
-    FILE_PATH_LITERAL("chrome-trace-config.json");
-
-base::FilePath GetTraceConfigFilePath() {
-#if defined(OS_ANDROID)
-  base::FilePath path(kAndroidTraceConfigDir);
-#elif defined(OS_POSIX) || defined(OS_WIN)
-  base::FilePath path;
-  PathService::Get(base::DIR_HOME, &path);
-#else
-  base::FilePath path;
-#endif
-  path = path.Append(kChromeConfigDir);
-  path = path.Append(kTraceConfigFileName);
-  return path;
-}
-
-} // namespace
-
-void EnableStartupTracingIfConfigFileExists() {
-  base::FilePath trace_config_file_path = GetTraceConfigFilePath();
-  if (!base::PathExists(trace_config_file_path))
-    return;
-
-  std::string trace_config_str;
-  if (!base::ReadFileToString(trace_config_file_path,
-                              &trace_config_str,
-                              kTraceConfigFileSizeLimit)) {
-    return;
-  }
-
-  base::trace_event::TraceConfig trace_config(trace_config_str);
-  base::trace_event::TraceLog::GetInstance()->SetEnabled(
-      trace_config, base::trace_event::TraceLog::RECORDING_MODE);
-}
-
-}  // namespace tracing