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 13 matching lines @@
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * 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/InstrumentingAgents.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() const
+{
+    if (hasObserverFor(PerformanceEntry::LongTask)

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

nit: we tend to prefer early bail-outs,
i.e. "if (!condition) return" as opposed to "if (condition) { ... }"

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

Ok. Done.

+        && !m_longTaskInspectorAgent) {
+        m_longTaskInspectorAgent = new InspectorWebPerfAgent(
+            InspectedFrames::create(frame()));
+        frame()->instrumentingAgents()->addInspectorWebPerfAgent(
+        m_longTaskInspectorAgent);
+    }
+}
+
+void Performance::disableLongTaskInstrumentation() const
+{
+    if (!hasObserverFor(PerformanceEntry::LongTask)
+        && m_longTaskInspectorAgent) {
+        frame()->instrumentingAgents()->removeInspectorWebPerfAgent(
+            m_longTaskInspectorAgent);
+        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