Make base::PendingTask support ConvertableToTraceFormat

base/pending_task.h

 // Copyright (c) 2011 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_PENDING_TASK_H_
 #define BASE_PENDING_TASK_H_
 
+#include <memory>
 #include <queue>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/location.h"
+#include "base/macros.h"
 #include "base/time/time.h"
+#include "base/trace_event/trace_event_impl.h"
 #include "base/tracking_info.h"
 
 namespace base {
 
 // Contains data about a pending task. Stored in TaskQueue and DelayedTaskQueue
 // for use by classes that queue and execute tasks.
 struct BASE_EXPORT PendingTask : public TrackingInfo {
+  // A thread-safe copy of a PendingTask's info required by tracing.
+  class TracingInfo : public trace_event::ConvertableToTraceFormat {

[caseq, 2016/09/29 22:46:37]

Why does it have to be nested class of PendingTask? This could as well be
somewhere else.

[gab, 2016/10/03 15:18:58]

Good point, I'll move it when we achieve overall consensus on what this CL is
doing.

+   public:
+    TracingInfo(const tracked_objects::Location& posted_from);
+    ~TracingInfo() override;
+
+    // Overridden from trace_event::ConvertableToTraceFormat:
+    void AppendAsTraceFormat(std::string* out) const override;
+
+   private:
+    const tracked_objects::Location posted_from_;
+
+    DISALLOW_COPY_AND_ASSIGN(TracingInfo);
+  };
+
   PendingTask(const tracked_objects::Location& posted_from,
               Closure task);
   PendingTask(const tracked_objects::Location& posted_from,
               Closure task,
               TimeTicks delayed_run_time,
               bool nestable);
   PendingTask(PendingTask&& other);
   ~PendingTask();
 
   PendingTask& operator=(PendingTask&& other);
 
   // Used to support sorting.
   bool operator<(const PendingTask& other) const;
 
+  std::unique_ptr<trace_event::ConvertableToTraceFormat> GetTracingInfo() const;

[caseq, 2016/09/29 22:46:37]

ditto.

[gab, 2016/10/03 15:18:58]

Acknowledged.

+
   // The task to run.
   Closure task;
 
   // The site this PendingTask was posted from.
   tracked_objects::Location posted_from;
 
   // Secondary sort key for run time.
   int sequence_num;
 
   // OK to dispatch from a nested loop.
   bool nestable;
 
   // Needs high resolution timers.
   bool is_high_res;
 };
 
 using TaskQueue = std::queue<PendingTask>;
 
 // PendingTasks are sorted by their |delayed_run_time| property.
 using DelayedTaskQueue = std::priority_queue<base::PendingTask>;
 
 }  // namespace base
 
 #endif  // BASE_PENDING_TASK_H_