enable / disable Long Task instrumentation based on presence of LongTask observer

third_party/WebKit/Source/core/timing/PerformanceBase.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 412 matching lines @@
 }
 
 void PerformanceBase::notifyObserversOfEntry(PerformanceEntry& entry)
 {
     for (auto& observer : m_observers) {
         if (observer->filterOptions() & entry.entryTypeEnum())
             observer->enqueuePerformanceEntry(entry);
     }
 }
 
-bool PerformanceBase::hasObserverFor(PerformanceEntry::EntryType filterType)
+bool PerformanceBase::hasObserverFor(PerformanceEntry::EntryType filterType) const
 {
     return m_observerFilterOptions & filterType;
 }
 
 void PerformanceBase::activateObserver(PerformanceObserver& observer)
 {
     if (m_activeObservers.isEmpty())
         m_deliverObservationsTimer.startOneShot(0, BLINK_FROM_HERE);
 
     m_activeObservers.add(&observer);
@@ skipping 62 matching lines @@
     visitor->trace(m_resourceTimingBuffer);
     visitor->trace(m_longTaskTimingBuffer);
     visitor->trace(m_userTiming);
     visitor->trace(m_observers);
     visitor->trace(m_activeObservers);
     visitor->trace(m_suspendedObservers);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink