Let Dart code running in Sky add events to the trace timeline

sky/engine/core/frame/Tracing.h

+// Copyright 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 SKY_ENGINE_CORE_FRAME_TRACING_H_
+#define SKY_ENGINE_CORE_FRAME_TRACING_H_
+
+#include "sky/engine/tonic/dart_wrappable.h"
+#include "sky/engine/wtf/PassRefPtr.h"
+#include "sky/engine/wtf/RefCounted.h"
+#include "sky/engine/wtf/text/WTFString.h"
+
+namespace blink {
+
+class Tracing : public RefCounted<Tracing>, public DartWrappable {
+    DEFINE_WRAPPERTYPEINFO();
+public:
+    ~Tracing() override;
+    static PassRefPtr<Tracing> create() { return adoptRef(new Tracing); }
+
+    void begin(const String& name);
+    void end(const String& name);
+
+private:
+    Tracing();
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_FRAME_TRACING_H_