GetTimeToCallback() returns estimated time to callback.

base/timer/timer.cc

 // Copyright (c) 2012 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/timer/timer.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 89 matching lines @@
 }
 
 bool Timer::IsRunning() const {
   return is_running_;
 }
 
 TimeDelta Timer::GetCurrentDelay() const {
   return delay_;
 }
 
+TimeDelta Timer::GetTimeToCallback() const {
+  if (!user_task_)
+    return TimeDelta::Max();
+  return scheduled_run_time_ - Now();
+}
+
 void Timer::SetTaskRunner(scoped_refptr<SingleThreadTaskRunner> task_runner) {
   // Do not allow changing the task runner once something has been scheduled.
   DCHECK_EQ(thread_id_, 0);
   task_runner_.swap(task_runner);
 }
 
 void Timer::Start(const tracked_objects::Location& posted_from,
                   TimeDelta delay,
                   const base::Closure& user_task) {
   SetTaskInfo(posted_from, delay, user_task);
@@ skipping 105 matching lines @@
     PostNewScheduledTask(delay_);
   else
     Stop();
 
   task.Run();
 
   // No more member accesses here: *this could be deleted at this point.
 }
 
 }  // namespace base