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/TraceLocation.h"
+
+namespace blink {
+
+class Scheduler;
+
+class TracedTask {
+public:
+    typedef Function<void()> Task;
+
+    void run() const;
+
+private:
+
+    // Constructor is private, with scheduler as a friend, to keep this
+    // class hidden to everyone apart from the scheduler.

[Sami, 2014/08/29 14:50:25]

This is a fairly common pattern in Blink so I don't think it needs a comment.

[picksi1, 2014/09/01 11:06:51]

Done.

+    friend Scheduler;

[Sami, 2014/08/29 14:50:25]

nit: People tend to write "friend class Scheduler".

[picksi1, 2014/09/01 11:06:51]

Done.

+    TracedTask(const Task&, const TraceLocation&, const char*, int);

[Sami, 2014/08/29 14:50:25]

Both const char* and int should have a name here.

|int| should match the type of m_flowTraceID.

[picksi1, 2014/09/01 11:06:51]

I'm keen to encapsulate the fact that a task ID ends up as an uint64_t inside
the TracedTask, as it feels like an implementation detail forced on us by the
MANGLE macro. I've kept the parameter an int and am explicitly casting it into a
uint64_t in the constructor.

+
+    unsigned long long m_FlowTraceID;

[Sami, 2014/08/29 14:50:25]

Lower caps for members: m_flowTraceID

This should probably be int64_t to match Chromium.

[picksi1, 2014/09/01 11:06:51]

Done.

+    Task m_task;
+    TraceLocation m_location;
+    const char * m_name;

[Sami, 2014/08/29 14:50:25]

No space before "*".

[picksi1, 2014/09/01 11:06:51]

Done.

+
+};
+
+} // namespace blink
+
+#endif // TracedTask_h