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

third_party/WebKit/Source/platform/scheduler/base/queueing_time_estimator.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_SOURCE_PLATFORM_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "public/platform/WebCommon.h"
 
+#include <memory>
+
 namespace base {
 class TickClock;
 }
 
 namespace blink {
 namespace scheduler {
 
 // Records the expected queueing time for a high priority task occurring
 // randomly during each interval of length |window_duration|.
 class BLINK_PLATFORM_EXPORT QueueingTimeEstimator {
  public:
   class BLINK_PLATFORM_EXPORT Client {
    public:
     virtual void OnQueueingTimeForWindowEstimated(
         base::TimeDelta queueing_time) = 0;
     Client() {}
     virtual ~Client() {}
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Client);
   };
 
   QueueingTimeEstimator(Client* client, base::TimeDelta window_duration);
 
-  void OnToplevelTaskCompleted(base::TimeTicks task_start_time,
+  void OnTopLevelTaskStarted(base::TimeTicks task_start_time);
+  void OnTopLevelTaskCompleted(base::TimeTicks task_start_time,
                                base::TimeTicks task_end_time);
 
+  base::TimeDelta EstimateQueueingTimeIncludingCurrentTask(base::TimeTicks now) const;
+
  private:
+  // Returns a clone of this object, with the |client_| set to |client|.
+  std::unique_ptr<QueueingTimeEstimator> CloneWithClient(Client* client) const;

[Sami, 2016/08/24 14:56:01]

Is it necessary for this to be a heap allocation? It seems like we could make
this a private copy constructor and keep the temporary class on the stack.

Alternatively we could split the computation backend from the client reporting
part and only copy the former, but I'm not sure if it would be worth it.

[tdresser, 2016/08/24 17:22:50]

Done.

   bool TimePastWindowEnd(base::TimeTicks task_end_time);
   Client* client_;  // NOT OWNED.
 
   base::TimeDelta current_expected_queueing_time_;
   base::TimeDelta window_duration_;
   base::TimeTicks window_start_time_;
 
+  // Only used when including active task in estimated queueing time.
+  base::TimeTicks current_task_start_time_;
+
   DISALLOW_COPY_AND_ASSIGN(QueueingTimeEstimator);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_