Force events to be non blocking if main thread is unresponsive.

third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc

 // Copyright 2014 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 "platform/scheduler/base/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 274 matching lines @@
     UpdateWorkQueues(&lazy_now);
 
     internal::WorkQueue* work_queue = nullptr;
     if (!SelectWorkQueueToService(&work_queue))
       break;
 
     // NB this may unregister the queue.
     switch (ProcessTaskFromWorkQueue(work_queue, is_nested, &lazy_now)) {
       case ProcessTaskResult::DEFERRED:
         // If a task was deferred, try again with another task.
+        DCHECK(delegate_->IsNested());
         continue;
       case ProcessTaskResult::EXECUTED:
         break;
       case ProcessTaskResult::TASK_QUEUE_MANAGER_DELETED:
         return;  // The TaskQueueManager got deleted, we must bail out.
     }
 
     // Only run a single task per batch in nested run loops so that we can
     // properly exit the nested loop when someone calls RunLoop::Quit().
     if (is_nested)
@@ skipping 331 matching lines @@
 }
 
 void TaskQueueManager::SetRecordTaskDelayHistograms(
     bool record_task_delay_histograms) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   record_task_delay_histograms_ = record_task_delay_histograms;
 }
 
 }  // namespace scheduler
 }  // namespace blink