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

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

 /*
  * 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 45 matching lines @@
 using PerformanceObservers = HeapListHashSet<Member<PerformanceObserver>>;
 
 class CORE_EXPORT PerformanceBase : public EventTargetWithInlineData {
 public:
     ~PerformanceBase() override;
 
     const AtomicString& interfaceName() const override;
 
     virtual PerformanceTiming* timing() const;
 
+    virtual void enableLongTaskInstrumentation() const {}
+    virtual void disableLongTaskInstrumentation() const {}

[caseq, 2016/09/15 23:29:40]

Why are these two const? I find it to be a bit artificial, considering you have
to use mutable in the implementaiton.

[panicker, 2016/09/16 17:07:58]

Done.

+
     // Reduce the resolution to 5µs to prevent timing attacks. See:
     // http://www.w3.org/TR/hr-time-2/#privacy-security
     static double clampTimeResolution(double timeSeconds);
 
     // Translate given platform monotonic time in seconds into a high resolution
     // DOMHighResTimeStamp in milliseconds. The result timestamp is relative to
     // document's time origin and has a time resolution that is safe for
     // exposing to web.
     DOMHighResTimeStamp monotonicTimeToDOMHighResTimeStamp(double) const;
     double monotonicTimeToDOMHighResTimeStampInMillis(DOMHighResTimeStamp) const;
@@ skipping 49 matching lines @@
     bool isResourceTimingBufferFull();
     void addResourceTimingBuffer(PerformanceEntry&);
 
     bool isFrameTimingBufferFull();
     void addFrameTimingBuffer(PerformanceEntry&);
 
     bool isLongTaskTimingBufferFull();
     void addLongTaskTimingBuffer(PerformanceEntry&);
 
     void notifyObserversOfEntry(PerformanceEntry&);
-    bool hasObserverFor(PerformanceEntry::EntryType);
+    bool hasObserverFor(PerformanceEntry::EntryType) const;
 
     void deliverObservationsTimerFired(TimerBase*);
 
     PerformanceEntryVector m_frameTimingBuffer;
     unsigned m_frameTimingBufferSize;
     PerformanceEntryVector m_resourceTimingBuffer;
     unsigned m_resourceTimingBufferSize;
     PerformanceEntryVector m_longTaskTimingBuffer;
     unsigned m_longTaskTimingBufferSize;
     Member<UserTiming> m_userTiming;
 
     double m_timeOrigin;
 
     PerformanceEntryTypeMask m_observerFilterOptions;
     PerformanceObservers m_observers;
     PerformanceObservers m_activeObservers;
     PerformanceObservers m_suspendedObservers;
     Timer<PerformanceBase> m_deliverObservationsTimer;
 };
 
 } // namespace blink
 
 #endif // PerformanceBase_h