Measure usage of JavaScript variables created from named elements.

third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp

Index: third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp b/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
index 774a91e6f608d2efff4e0b965676289fd4b1455b..feb1196c4c3cd6e17c99ba01a3264fb997511055 100644
--- a/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
@@ -377,12 +377,15 @@ void V8Window::namedPropertyGetterCustom(
 
   if (!hasNamedItem && hasIdItem &&
       !doc->containsMultipleElementsWithId(name)) {
+    UseCounter::count(doc, UseCounter::DOMClobberedVariableAccessed);
     v8SetReturnValueFast(info, doc->getElementById(name), window);
     return;
   }
 
   HTMLCollection* items = doc->windowNamedItems(name);
   if (!items->isEmpty()) {
+    UseCounter::count(doc, UseCounter::DOMClobberedVariableAccessed);
+
     // TODO(esprehn): Firefox doesn't return an HTMLCollection here if there's
     // multiple with the same name, but Chrome and Safari does. What's the
     // right behavior?