Measure usage of JavaScript variables created from named elements.

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

 /*
  * Copyright (C) 2009, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 359 matching lines @@
     return;
 
   bool hasNamedItem = toHTMLDocument(doc)->hasNamedItem(name);
   bool hasIdItem = doc->hasElementWithId(name);
 
   if (!hasNamedItem && !hasIdItem)
     return;
 
   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?
     if (items->hasExactlyOneItem()) {
       v8SetReturnValueFast(info, items->item(0), window);
       return;
     }
     v8SetReturnValueFast(info, items, window);
     return;
   }
 }
 
 }  // namespace blink