Add detailed use counters for document.registerElement use.

third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp b/third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp
index 4fec07e9ade03663218fbb0aa63aaa693b1cd170..cd292725b55cd96441cb30c71529b00136da794a 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp
@@ -48,6 +48,7 @@
 #include "core/dom/custom/V0CustomElementDescriptor.h"
 #include "core/dom/custom/V0CustomElementException.h"
 #include "core/dom/custom/V0CustomElementProcessingStack.h"
+#include "core/frame/UseCounter.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
@@ -354,6 +355,9 @@ static void constructCustomElement(
       namespaceURI, tagName,
       StringOrDictionary::fromString(maybeType->IsNull() ? nullAtom : type),
       exceptionState);
+  if (element) {
+    UseCounter::count(document, UseCounter::V0CustomElementsConstruct);
+  }
   v8SetReturnValueFast(info, element, document);
 }