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

third_party/WebKit/Source/core/timing/Performance.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 15 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/timing/Performance.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
+#include "core/inspector/InspectedFrames.h"
+#include "core/inspector/InspectorWebPerfAgent.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/timing/PerformanceTiming.h"
 
 namespace blink {
 
 static double toTimeOrigin(LocalFrame* frame)
 {
     if (!frame)
         return 0.0;
 
@@ skipping 39 matching lines @@
 }
 
 PerformanceTiming* Performance::timing() const
 {
     if (!m_timing)
         m_timing = PerformanceTiming::create(m_frame);
 
     return m_timing.get();
 }
 
+void Performance::enableLongTaskInstrumentation()
+{
+    if (!hasObserverFor(PerformanceEntry::LongTask) || m_longTaskInspectorAgent)
+        return;
+    m_longTaskInspectorAgent = new InspectorWebPerfAgent(
+        InspectedFrames::create(frame()));
+    m_longTaskInspectorAgent->enable();
+}
+
+void Performance::disableLongTaskInstrumentation()
+{
+    if (hasObserverFor(PerformanceEntry::LongTask) || !m_longTaskInspectorAgent)

[dgozman, 2016/09/19 17:55:59]

Since we check for enable conditions in both methods, I think we can combine
them into a single updateLongTaskInstrumentation which will either enable or
disable or do nothing.

[panicker, 2016/09/20 12:00:39]

Done.

+        return;
+    m_longTaskInspectorAgent->disable();
+    m_longTaskInspectorAgent = nullptr;
+}
+
 DEFINE_TRACE(Performance)
 {
     visitor->trace(m_navigation);
     visitor->trace(m_timing);
+    visitor->trace(m_longTaskInspectorAgent);
     DOMWindowProperty::trace(visitor);
     PerformanceBase::trace(visitor);
 }
 
 } // namespace blink