Report expected task queueing time via UMA

base/message_loop/message_loop.h

Index: base/message_loop/message_loop.h
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index 8e73d42b1e278dac9f68a58eeb1a01af84f6149e..7f991decdb7a87bbff7d868c63fc3e53f43eb1e6 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -171,6 +171,17 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate {
   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).
   //
@@ -509,6 +520,8 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate {
 
   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_;