Add option to export tracing events to ETW.

base/trace_event/trace_event_etw_export_win.h

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.

[Lei Zhang, 2015/04/15 08:10:36]

nit: no (c)

[Georges Khalil, 2015/04/15 15:10:32]

Done (same in .cc too).

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file contains the Windows-specific exporting to ETW.
+#ifndef BASE_TRACE_EVENT_TRACE_ETW_EXPORT_H_
+#define BASE_TRACE_EVENT_TRACE_ETW_EXPORT_H_
+
+#include "base/base_export.h"
+#include "base/trace_event/trace_event_impl.h"
+
+// Fwd.
+template <typename Type>
+struct StaticMemorySingletonTraits;
+
+namespace base {
+namespace trace_event {
+
+class BASE_EXPORT TraceEventETWExport {
+ public:
+  ~TraceEventETWExport();
+
+  // Retrieves the singleton.
+  // Note that this may return NULL post-AtExit processing.
+  static TraceEventETWExport* GetInstance();
+
+  static void EnableETWExport();
+  static void DisableETWExport();
+
+  static bool isETWExportEnabled() { return GetInstance()->ETWExportEnabled_; }
+
+  static void AddEvent(

[Lei Zhang, 2015/04/15 08:10:36]

The above methods seem more obvious, but AddEvent() and AddCustomEvent() can use
some documentation.

[Georges Khalil, 2015/04/15 15:10:32]

I added documentation for all functions. Should be clearer now.

+      char phase,
+      const unsigned char* category_group_enabled,
+      const char* name,
+      unsigned long long id,
+      int num_args,
+      const char** arg_names,
+      const unsigned char* arg_types,
+      const unsigned long long* arg_values,
+      const scoped_refptr<ConvertableToTraceFormat>* convertable_values);
+
+  static void AddCustomEvent(const char* name,

[Lei Zhang, 2015/04/15 08:10:36]

This doesn't seem to have any callers?

[Georges Khalil, 2015/04/15 15:10:32]

Not yet, this is used to add an event that is only exported to ETW (and not
to the internal tracer). Eventually, I'm planning on having multiple
providers, but for now, it shares the same one as the internal events (they
all appear on the same series when visualized).

+                             char const* phase,
+                             const char* arg_name_1,
+                             const char* arg_value_1,
+                             const char* arg_name_2,
+                             const char* arg_value_2,
+                             const char* arg_name_3,
+                             const char* arg_value_3);
+
+  void Resurrect();
+
+ private:
+  bool ETWExportEnabled_;
+  // Ensure only the provider can construct us.
+  friend struct StaticMemorySingletonTraits<TraceEventETWExport>;
+  TraceEventETWExport();
+
+  DISALLOW_COPY_AND_ASSIGN(TraceEventETWExport);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_TRACE_ETW_EXPORT_H_