Update from https://crrev.com/328418

base/message_loop/incoming_task_queue.cc

 // Copyright 2013 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/incoming_task_queue.h"
 
 #include <limits>
 
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 26 matching lines @@
 #endif
 }
 
 }  // namespace
 
 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
     : high_res_task_count_(0),
       message_loop_(message_loop),
       next_sequence_num_(0),
       message_loop_scheduled_(false),
-      always_schedule_work_(AlwaysNotifyPump(message_loop_->type())) {
+      always_schedule_work_(AlwaysNotifyPump(message_loop_->type())),
+      is_ready_for_scheduling_(false) {
 }
 
 bool IncomingTaskQueue::AddToIncomingQueue(
     const tracked_objects::Location& from_here,
     const Closure& task,
     TimeDelta delay,
     bool nestable) {
   DLOG_IF(WARNING,
           delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
       << "Requesting super-long task delay period of " << delay.InSeconds()
@@ skipping 44 matching lines @@
   int high_res_tasks = high_res_task_count_;
   high_res_task_count_ = 0;
   return high_res_tasks;
 }
 
 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
   AutoLock lock(incoming_queue_lock_);
   message_loop_ = NULL;
 }
 
+void IncomingTaskQueue::StartScheduling() {
+  AutoLock lock(incoming_queue_lock_);
+  DCHECK(!is_ready_for_scheduling_);
+  DCHECK(!message_loop_scheduled_);
+  is_ready_for_scheduling_ = true;
+  if (!incoming_queue_.empty())
+    ScheduleWork();
+}
+
 IncomingTaskQueue::~IncomingTaskQueue() {
   // Verify that WillDestroyCurrentMessageLoop() has been called.
   DCHECK(!message_loop_);
 }
 
 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
   TimeTicks delayed_run_time;
   if (delay > TimeDelta())
     delayed_run_time = TimeTicks::Now() + delay;
   else
@@ skipping 19 matching lines @@
   // delayed_run_time value) and for identifying the task in about:tracing.
   pending_task->sequence_num = next_sequence_num_++;
 
   message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
                                                 *pending_task);
 
   bool was_empty = incoming_queue_.empty();
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
-  if (always_schedule_work_ || (!message_loop_scheduled_ && was_empty)) {
-    // Wake up the message loop.
-    message_loop_->ScheduleWork();
-    // After we've scheduled the message loop, we do not need to do so again
-    // until we know it has processed all of the work in our queue and is
-    // waiting for more work again. The message loop will always attempt to
-    // reload from the incoming queue before waiting again so we clear this flag
-    // in ReloadWorkQueue().
-    message_loop_scheduled_ = true;
+  if (is_ready_for_scheduling_ &&
+      (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
+    ScheduleWork();
   }
 
   return true;
 }
 
+void IncomingTaskQueue::ScheduleWork() {
+  DCHECK(is_ready_for_scheduling_);
+  // Wake up the message loop.
+  message_loop_->ScheduleWork();
+  // After we've scheduled the message loop, we do not need to do so again
+  // until we know it has processed all of the work in our queue and is
+  // waiting for more work again. The message loop will always attempt to
+  // reload from the incoming queue before waiting again so we clear this flag
+  // in ReloadWorkQueue().
+  message_loop_scheduled_ = true;
+}
+
 }  // namespace internal
 }  // namespace base