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

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

Index: third_party/WebKit/Source/core/timing/PerformanceBase.h
diff --git a/third_party/WebKit/Source/core/timing/PerformanceBase.h b/third_party/WebKit/Source/core/timing/PerformanceBase.h
index 463faf12043d5c14d5a53361cd21ad5c543977d0..8efd743f0c1625aa17cba51ede5f23a630fdea02 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceBase.h
+++ b/third_party/WebKit/Source/core/timing/PerformanceBase.h
@@ -63,6 +63,9 @@ public:
 
     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);
@@ -132,7 +135,7 @@ protected:
     void addLongTaskTimingBuffer(PerformanceEntry&);
 
     void notifyObserversOfEntry(PerformanceEntry&);
-    bool hasObserverFor(PerformanceEntry::EntryType);
+    bool hasObserverFor(PerformanceEntry::EntryType) const;
 
     void deliverObservationsTimerFired(TimerBase*);