Revert of Revert 221427 "Add instrumentation to the MessagePumpMac family ..."

base/message_loop/message_pump.h

Index: base/message_loop/message_pump.h
diff --git a/base/message_loop/message_pump.h b/base/message_loop/message_pump.h
index 4dc501b660839e0a56b74778abc883864396847d..a795f31b67ccebf6c92161292906771493fa5f25 100644
--- a/base/message_loop/message_pump.h
+++ b/base/message_loop/message_pump.h
@@ -12,6 +12,7 @@
 
 namespace base {
 
+class TimeDelta;
 class TimeTicks;
 
 class BASE_EXPORT MessagePump : public NonThreadSafe {
@@ -41,6 +42,19 @@
     // Called from within Run just before the message pump goes to sleep.
     // Returns true to indicate that idle work was done.
     virtual bool DoIdleWork() = 0;
+
+    // Via the two required out pointers, returns the length of the Delegate's
+    // work queue and the length of time that the first item in the queue has
+    // been waiting to run. If the work queue is empty, the count and delay
+    // will both be zero.
+    // Note that this only counts the tasks in the ready-to-run queue and not
+    // the incoming queue that is used by other threads to post tasks. The
+    // latter queue requires holding a lock, which is deemed too expensive for
+    // instrumentation code. Under normal conditions, the incoming queue should
+    // be small or zero, but under heavy loads it may be much larger and
+    // |queue_count| may be up to 1/4 the size of the incoming queue.
+    virtual void GetQueueingInformation(size_t* queue_count,
+                                        TimeDelta* queueing_delay) {}
   };
 
   MessagePump();