Add use counters for elements used in Shadow DOM

third_party/WebKit/Source/core/html/HTMLShadowElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLShadowElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLShadowElement.cpp b/third_party/WebKit/Source/core/html/HTMLShadowElement.cpp
index 309a51901a6c9ddc15abf28251c48ce998d99626..1507906f69c94586c880e4a82160be8f12aa99a8 100644
--- a/third_party/WebKit/Source/core/html/HTMLShadowElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLShadowElement.cpp
@@ -33,6 +33,7 @@
 #include "core/HTMLNames.h"
 #include "core/dom/Document.h"
 #include "core/dom/shadow/ShadowRoot.h"
+#include "core/frame/UseCounter.h"
 #include "core/inspector/ConsoleMessage.h"
 
 namespace blink {
@@ -40,7 +41,9 @@ namespace blink {
 class Document;
 
 inline HTMLShadowElement::HTMLShadowElement(Document& document)
-    : InsertionPoint(HTMLNames::shadowTag, document) {}
+    : InsertionPoint(HTMLNames::shadowTag, document) {
+  UseCounter::count(document, UseCounter::HTMLShadowElement);
+}
 
 DEFINE_NODE_FACTORY(HTMLShadowElement)