Presentation API: add UMA.

Source/modules/presentation/PresentationAvailability.cpp

Index: Source/modules/presentation/PresentationAvailability.cpp
diff --git a/Source/modules/presentation/PresentationAvailability.cpp b/Source/modules/presentation/PresentationAvailability.cpp
index 4d4600879db940a0a1e27f57bce3ff3eae20b382..e0537d6b0c8ab95029c36dd5911bc84f8528b8f3 100644
--- a/Source/modules/presentation/PresentationAvailability.cpp
+++ b/Source/modules/presentation/PresentationAvailability.cpp
@@ -8,6 +8,7 @@
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/Document.h"
 #include "core/events/Event.h"
+#include "core/frame/UseCounter.h"
 #include "modules/EventTargetModulesNames.h"
 #include "modules/presentation/PresentationController.h"
 #include "public/platform/Platform.h"
@@ -62,6 +63,14 @@ ExecutionContext* PresentationAvailability::executionContext() const
     return ActiveDOMObject::executionContext();
 }
 
+bool PresentationAvailability::addEventListener(const AtomicString& eventType, PassRefPtrWillBeRawPtr<EventListener> listener, bool capture)
+{
+    if (eventType == EventTypeNames::change)
+        UseCounter::count(executionContext(), UseCounter::PresentationAvailabilityChangeEventListener);
+
+    return EventTarget::addEventListener(eventType, listener, capture);
+}
+
 void PresentationAvailability::availabilityChanged(bool value)
 {
     if (m_value == value)