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

third_party/WebKit/public/platform/scheduler/base/task_time_observer.h

 // Copyright 2016 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.
 
 #ifndef THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_
 #define THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_
 
 #include "base/time/time.h"
 #include "public/platform/WebCommon.h"
 
 namespace blink {
 namespace scheduler {
 
 class TaskQueue;
 
 // TaskTimeObserver provides an API for observing completion of renderer tasks.
 class BLINK_PLATFORM_EXPORT TaskTimeObserver {
  public:
   TaskTimeObserver() {}
   virtual ~TaskTimeObserver() {}
 
+  // Callback to be called when task is started.
+  // |task_queue| - TaskQueue on which this task was run,
+  // |start_time| - time in seconds when task started to run,
+  virtual void ReportTaskStartTime(double start_time) {}
+
   // Callback to be called when task is completed.
   // |task_queue| - TaskQueue on which this task was run,
   // |start_time| - time in seconds when task started to run,
   // |end_time| - time in seconds when task was completed.
-  virtual void ReportTaskTime(TaskQueue* task_queue,
-                              double start_time,
-                              double end_time) = 0;
+  virtual void ReportTaskEndTime(TaskQueue* task_queue,
+                                 double start_time,
+                                 double end_time) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TaskTimeObserver);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_