Document and measure the TextEvent interface and the textinput event

Source/core/events/EventTarget.cpp

Index: Source/core/events/EventTarget.cpp
diff --git a/Source/core/events/EventTarget.cpp b/Source/core/events/EventTarget.cpp
index 501752209c6707590d69250dbcadf0f07e9ab2ec..b009b1d9fc772dfa35e4d3bff65852357e35db86 100644
--- a/Source/core/events/EventTarget.cpp
+++ b/Source/core/events/EventTarget.cpp
@@ -327,6 +327,9 @@ void EventTarget::fireEventListeners(Event* event, EventTargetData* d, EventList
     } else if (event->type() == EventTypeNames::focusin || event->type() == EventTypeNames::focusout) {
         if (LocalDOMWindow* executingWindow = this->executingWindow())
             UseCounter::count(executingWindow->document(), UseCounter::FocusInOutEvent);
+    } else if (event->type() == EventTypeNames::textInput) {
+        if (LocalDOMWindow* executingWindow = this->executingWindow())
+            UseCounter::count(executingWindow->document(), UseCounter::TextInputFired);
     }
 
     size_t i = 0;