Report expected task queueing time via UMA

base/message_loop/message_loop.h

 // Copyright 2013 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_MESSAGE_LOOP_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
 
 #include <memory>
 #include <queue>
 #include <string>
@@ skipping 153 matching lines @@
    public:
     virtual void OnBeginNestedMessageLoop() = 0;
 
    protected:
     virtual ~NestingObserver();
   };
 
   void AddNestingObserver(NestingObserver* observer);
   void RemoveNestingObserver(NestingObserver* observer);
 
+  class BASE_EXPORT RecentTimeObserver {
+   public:
+    virtual void OnUpdateRecentTime(base::TimeTicks recent_time) = 0;
+
+   protected:
+    virtual ~RecentTimeObserver();
+  };
+
+  void AddRecentTimeObserver(RecentTimeObserver* observer);
+  void RemoveRecentTimeObserver(RecentTimeObserver* observer);
+
   // NOTE: Deprecated; prefer task_runner() and the TaskRunner interfaces.
   // TODO(skyostil): Remove these functions (crbug.com/465354).
   //
   // The "PostTask" family of methods call the task's Run method asynchronously
   // from within a message loop at some point in the future.
   //
   // With the PostTask variant, tasks are invoked in FIFO order, inter-mixed
   // with normal UI or IO event processing.  With the PostDelayedTask variant,
   // tasks are called after at least approximately 'delay_ms' have elapsed.
   //
@@ skipping 318 matching lines @@
 
   // A queue of non-nestable tasks that we had to defer because when it came
   // time to execute them we were in a nested message loop.  They will execute
   // once we're out of nested message loops.
   TaskQueue deferred_non_nestable_work_queue_;
 
   ObserverList<DestructionObserver> destruction_observers_;
 
   ObserverList<NestingObserver> nesting_observers_;
 
+  ObserverList<RecentTimeObserver> recent_time_observers_;
+
   // A recursion block that prevents accidentally running additional tasks when
   // insider a (accidentally induced?) nested message pump.
   bool nestable_tasks_allowed_;
 
   // pump_factory_.Run() is called to create a message pump for this loop
   // if type_ is TYPE_CUSTOM and pump_ is null.
   MessagePumpFactoryCallback pump_factory_;
 
   std::string thread_name_;
   // A profiling histogram showing the counts of various messages and events.
@@ skipping 159 matching lines @@
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 static_assert(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
               "MessageLoopForIO should not have extra member variables");
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_