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

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

 // Copyright 2015 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.
 
 #include "core/timing/PerformanceObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/timing/PerformanceBase.h"
 #include "core/timing/PerformanceEntry.h"
@@ skipping 39 matching lines @@
     m_filterOptions = entryTypes;
     if (m_isRegistered)
         m_performance->updatePerformanceObserverFilterOptions();
     else
         m_performance->registerPerformanceObserver(*this);
     m_isRegistered = true;
 }
 
 void PerformanceObserver::disconnect()
 {
-    if (m_performance)
+    if (m_performance) {
         m_performance->unregisterPerformanceObserver(*this);
-
+    }
     m_performanceEntries.clear();
     m_isRegistered = false;
 }
 
 void PerformanceObserver::enqueuePerformanceEntry(PerformanceEntry& entry)
 {
     ASSERT(isMainThread());
     m_performanceEntries.append(&entry);
     if (m_performance)
         m_performance->activateObserver(*this);
@@ skipping 19 matching lines @@
 }
 
 DEFINE_TRACE(PerformanceObserver)
 {
     visitor->trace(m_callback);
     visitor->trace(m_performance);
     visitor->trace(m_performanceEntries);
 }
 
 } // namespace blink