Layout Tests: Remove stringifyDOMObject() helper

third_party/WebKit/LayoutTests/resources/testharness-helpers.js

 /*
  * testharness-helpers contains various useful extensions to testharness.js to
  * allow them to be used across multiple tests before they have been
  * upstreamed. This file is intended to be usable from both document and worker
  * environments, so code should for example not rely on the DOM.
  */
 
 // Returns a promise that fulfills after the provided |promise| is fulfilled.
 // The |test| succeeds only if |promise| rejects with an exception matching
 // |code|. Accepted values for |code| follow those accepted for assert_throws().
@@ skipping 13 matching lines @@
   return promise.then(
     function() {
       throw 'assert_promise_rejects: ' + description + ' Promise did not reject.';
     },
     function(e) {
       if (code !== undefined) {
         assert_throws(code, function() { throw e; }, description);
       }
     });
 }
-
-// Stringifies a DOM object.  This function stringifies not only own properties
-// but also DOM attributes which are on a prototype chain.  Note that
-// JSON.stringify only stringifies own properties.
-function stringifyDOMObject(object)
-{
-    function deepCopy(src) {
-        if (typeof src != "object")
-            return src;
-        var dst = Array.isArray(src) ? [] : {};
-        for (var property in src) {
-            dst[property] = deepCopy(src[property]);
-        }
-        return dst;
-    }
-    return JSON.stringify(deepCopy(object));
-}