Always use the topmost delayed task as the basis for our WM_TIMER....

base/message_loop.cc

 // Copyright (c) 2006-2008 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.
 
 #include "base/message_loop.h"
 
 #include <algorithm>
 
 #include "base/compiler_specific.h"
 #include "base/lazy_instance.h"
@@ skipping 366 matching lines @@
   for (;;) {
     ReloadWorkQueue();
     if (work_queue_.empty())
       break;
 
     // Execute oldest task.
     do {
       PendingTask pending_task = work_queue_.front();
       work_queue_.pop();
       if (!pending_task.delayed_run_time.is_null()) {
-        bool was_empty = delayed_work_queue_.empty();
         AddToDelayedWorkQueue(pending_task);
-        if (was_empty)  // We only schedule the next delayed work item.
+        // If we changed the topmost task, then it is time to re-schedule.
+        if (delayed_work_queue_.top().task == pending_task.task)
           pump_->ScheduleDelayedWork(pending_task.delayed_run_time);
       } else {
         if (DeferOrRunPendingTask(pending_task))
           return true;
       }
     } while (!work_queue_.empty());
   }
 
   // Nothing happened.
   return false;
@@ skipping 175 matching lines @@
 
 void MessageLoopForIO::WatchSocket(int socket, short interest_mask, 
                                    struct event* e, Watcher* watcher) {
   pump_libevent()->WatchSocket(socket, interest_mask, e, watcher);
 }
 
 void MessageLoopForIO::UnwatchSocket(struct event* e) {
   pump_libevent()->UnwatchSocket(e);
 }
 #endif