Enable startup tracing from command line flags in components/tracing

components/tracing/common/trace_startup.cc

Index: components/tracing/common/trace_startup.cc
diff --git a/components/tracing/common/trace_startup.cc b/components/tracing/common/trace_startup.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2c8ae37025cf15ee8e19e057ecf64b412f6bdecd
--- /dev/null
+++ b/components/tracing/common/trace_startup.cc
@@ -0,0 +1,48 @@
+// 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.
+
+#include "components/tracing/common/trace_startup.h"
+
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/trace_log.h"
+#include "components/tracing/common/trace_config_file.h"
+#include "components/tracing/common/trace_to_console.h"
+#include "components/tracing/common/tracing_switches.h"
+
+namespace tracing {
+
+void EnableStartupTracingIfNeeded(bool can_access_file_system) {
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+
+  // Enables heap profiling if "--enable-heap-profiling" flag is passed.
+  base::trace_event::MemoryDumpManager::GetInstance()
+      ->EnableHeapProfilingIfNeeded();
+
+  if (command_line.HasSwitch(switches::kTraceStartup)) {
+    base::trace_event::TraceConfig trace_config(
+        command_line.GetSwitchValueASCII(switches::kTraceStartup),
+        base::trace_event::RECORD_UNTIL_FULL);
+    base::trace_event::TraceLog::GetInstance()->SetEnabled(
+        trace_config, base::trace_event::TraceLog::RECORDING_MODE);
+  } else if (command_line.HasSwitch(switches::kTraceToConsole)) {
+    base::trace_event::TraceConfig trace_config =
+        tracing::GetConfigForTraceToConsole();
+    LOG(ERROR) << "Start " << switches::kTraceToConsole
+               << " with CategoryFilter '"
+               << trace_config.ToCategoryFilterString() << "'.";
+    base::trace_event::TraceLog::GetInstance()->SetEnabled(
+        trace_config, base::trace_event::TraceLog::RECORDING_MODE);
+  } else if (can_access_file_system &&
+             tracing::TraceConfigFile::GetInstance()->IsEnabled()) {
+    // This checks kTraceConfigFile switch.
+    base::trace_event::TraceLog::GetInstance()->SetEnabled(
+        tracing::TraceConfigFile::GetInstance()->GetTraceConfig(),
+        base::trace_event::TraceLog::RECORDING_MODE);
+  }
+}
+
+}  // namespace tracing