Add basic tracing support to the gtest launcher

base/test/launcher/test_launcher_tracer.h

+// Copyright 2016 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 BASE_TEST_LAUNCHER_TEST_LAUNCHER_TRACER_H_
+#define BASE_TEST_LAUNCHER_TEST_LAUNCHER_TRACER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+
+class FilePath;
+
+// Records traces of test execution, e.g. to analyze performance.
+// Thread safe.
+class TestLauncherTracer {
+ public:
+  TestLauncherTracer();
+  ~TestLauncherTracer();
+
+  // Records an event corresponding to test process execution.
+  void RecordProcessExecution(TimeTicks start_time, TimeDelta duration);
+
+  // Dumps trace data as JSON. Returns true on success.
+  bool Dump(const FilePath& path) WARN_UNUSED_RESULT;
+
+ private:
+  // Simplified version of base::TraceEvent.
+  struct Event {
+    std::string name;  // Displayed name.

[Primiano Tucci (use gerrit), 2016/07/01 11:34:30]

Is this git cl formatted? I thought that it does align the comments. 

[Paweł Hajdan Jr., 2016/07/01 12:47:32]

Ah, that's a good point. I ran the CL through "git cl format" now.

+    TimeTicks timestamp;  // Timestamp when this event began.
+    TimeDelta duration;  // How long was this event.
+    PlatformThreadId thread_id;  // Thread ID where event was reported.
+  };
+
+  // Timestamp when tracing started.
+  TimeTicks trace_start_time_;
+
+  // Log of trace events.
+  std::vector<Event> events_;
+
+  // Lock to protect all member variables.
+  Lock lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestLauncherTracer);
+};
+
+}  // namespace base
+
+#endif  // BASE_TEST_LAUNCHER_TEST_LAUNCHER_TRACER_H_