Add instrumentation to the MessagePumpMac family of classes.

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 0ebba3a3e60ccfd07abb2808e2632a254a76747c..b2af6985f0b0e7c6710eb599466176c8a07ae752 100644
--- a/base/message_loop/message_pump.h
+++ b/base/message_loop/message_pump.h
@@ -6,10 +6,12 @@
 #define BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
 
 #include "base/base_export.h"
+#include "base/basictypes.h"
 #include "base/threading/non_thread_safe.h"
 
 namespace base {
 
+class TimeDelta;
 class TimeTicks;
 
 class BASE_EXPORT MessagePump : public NonThreadSafe {
@@ -39,6 +41,13 @@ class BASE_EXPORT MessagePump : public NonThreadSafe {
     // 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

[jar (doing other things), 2013/09/04 01:20:17]

nit: You already know this... and we talked about it in the code... but....

It only returns the length of the internalized work-queue, not the full queue,
for which (on average) less than half the queued tasks are recorded.  When work
loads are small, then this may be the entire queue (typically 0 queued items). 
When work loads are large, then there will (when the system is stable) be about
N tasks in the external (unmeasured) queue, and between 0 and N tasks (average
around N/2) tasks in the internal queue.

As a result, I think this metric will (on average) return a number that is 1/4th
the queue size (when it returns any size at all)... and of course 0 is 1/4th of
0... so it probably always returns a metric that is 1/4th of reality (on
average).

+    // been waiting to run. If the work queue is empty, the count and delay
+    // will both be zero.
+    virtual void GetQueueingInformation(size_t* queue_count,
+                                        TimeDelta* queueing_delay) {}
   };
 
   MessagePump();