Adding flow traces for blink scheduler events

Source/platform/scheduler/TracedTask.h

+// Copyright 2014 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 TracedTask_h
+#define TracedTask_h
+
+#include "platform/Task.h"
+#include "platform/TraceEvent.h"
+#include "platform/TraceLocation.h"
+
+namespace blink {
+
+#ifdef MANGLE_COMPILES_ON_WIN_OK
+// TODO: Once win version compiles correctly when using TRACE_ID_MANGLE remove
+// the ifdef to always mangle
+#define MANGLE(id) TRACE_ID_MANGLE(id)
+#else
+#define MANGLE(id) (id)
+#endif
+
+class TracedTask {
+public:
+    typedef Function<void()> Task;
+
+    void run() const;
+
+private:
+    friend class Scheduler;
+    TracedTask(const Task&, const TraceLocation&, const char* traceName);
+
+    // Declared volatile as it is atomically incremented.
+    static volatile int s_nextFlowTraceID;
+
+    uint64_t m_flowTraceID;
+    Task m_task;
+    TraceLocation m_location;
+    const char* m_traceName;
+};
+
+} // namespace blink
+
+#endif // TracedTask_h