base: Factor task debug annotations out of MessageLoop

base/debug/task_annotator.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 BASE_DEBUG_TASK_ANNOTATOR_H_
+#define BASE_DEBUG_TASK_ANNOTATOR_H_
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+
+namespace base {
+struct PendingTask;
+namespace debug {
+
+// Implements common debug annotations for posted tasks. This includes data
+// such as task origins, queueing durations and memory usage.
+class BASE_EXPORT TaskAnnotator {
+ public:
+  TaskAnnotator();
+  ~TaskAnnotator();
+
+  // Called to indicate that a task has been queued to run in the future.
+  // |queue_function| is used as the trace flow event name.
+  void DidQueueTask(const char* queue_function,
+                    const PendingTask& pending_task);
+
+  // Run a previously queued task. |queue_function| should match what was
+  // passed into |DidQueueTask| for this task. |run_function| is used as the
+  // name for the trace event that surrounds the task's execution.
+  void RunTask(const char* queue_function,
+               const char* run_function,
+               const PendingTask& pending_task);
+
+ private:
+  // Creates a process-wide unique ID to represent this task in trace events.
+  // This will be mangled with a Process ID hash to reduce the likelyhood of
+  // colliding with TaskAnnotator pointers on other processes.
+  uint64 GetTaskTraceID(const PendingTask& task) const;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskAnnotator);
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_TASK_ANNOTATOR_H_