webrtc: Fixes WebRtcBrowserTest to use DOM attributes correctly.

chrome/test/data/webrtc/peerconnection.js

 /**
  * Copyright 2014 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /**
  * We need a STUN server for some API calls.
  * @private
  */
@@ skipping 39 matching lines @@
  * Returns a string on the format ok-(JSON encoded session description).
  *
  * @param {!Object} constraints Any createOffer constraints.
  */
 function createLocalOffer(constraints) {
   peerConnection_().createOffer(
       function(localOffer) {
         success_('createOffer');
         setLocalDescription(peerConnection, localOffer);
 
-        returnToTest('ok-' + JSON.stringify(localOffer));
+        returnToTest('ok-' + stringifyDOMObject_(localOffer));
       },
       function(error) { failure_('createOffer', error); },
       constraints);
 }
 
 /**
  * Asks this page to accept an offer and generate an answer.
  *
  * Returns a string on the format ok-(JSON encoded session description).
  *
@@ skipping 11 matching lines @@
   var sessionDescription = new RTCSessionDescription(offer);
   peerConnection_().setRemoteDescription(
       sessionDescription,
       function() { success_('setRemoteDescription'); },
       function(error) { failure_('setRemoteDescription', error); });
 
   peerConnection_().createAnswer(
       function(answer) {
         success_('createAnswer');
         setLocalDescription(peerConnection, answer);
-        returnToTest('ok-' + JSON.stringify(answer));
+        returnToTest('ok-' + stringifyDOMObject_(answer));
       },
       function(error) { failure_('createAnswer', error); },
       constraints);
 }
 
 /**
  * Asks this page to accept an answer generated by the peer in response to a
  * previous offer by this page
  *
  * Returns a string ok-accepted-answer on success.
@@ skipping 68 matching lines @@
  *
  * Returns a JSON-encoded array of RTCIceCandidate instances to the test.
  */
 function getAllIceCandidates() {
   if (peerConnection_().iceGatheringState != 'complete') {
     console.log('Still ICE gathering - waiting...');
     setTimeout(getAllIceCandidates, 100);
     return;
   }
 
-  returnToTest(JSON.stringify(gIceCandidates));
+  returnToTest(stringifyDOMObject_(gIceCandidates));
 }
 
 /**
  * Receives ICE candidates from the peer.
  *
  * Returns ok-received-candidates to the test on success.
  *
  * @param iceCandidatesJson a JSON-encoded array of RTCIceCandidate instances.
  */
 function receiveIceCandidates(iceCandidatesJson) {
@@ skipping 46 matching lines @@
   return gPeerConnection;
 }
 
 /** @private */
 function success_(method) {
   debug(method + '(): success.');
 }
 
 /** @private */
 function failure_(method, error) {
-  throw failTest(method + '() failed: ' + JSON.stringify(error));
+  throw failTest(method + '() failed: ' + stringifyDOMObject_(error));
 }
 
 /** @private */
 function iceCallback_(event) {
   if (event.candidate)
     gIceCandidates.push(event.candidate);
 }
 
 /** @private */
 function setLocalDescription(peerConnection, sessionDescription) {
@@ skipping 14 matching lines @@
   attachMediaStream(videoTag, event.stream);
 }
 
 /** @private */
 function removeStreamCallback_(event) {
   debug('Call ended.');
   document.getElementById('remote-view').src = '';
 }
 
 /**
+ * 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.
+ * @private
+ */
+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));
+}
+
+/**
  * Parses JSON-encoded session descriptions and ICE candidates.
  * @private
  */
 function parseJson_(json) {
   // Escape since the \r\n in the SDP tend to get unescaped.
   jsonWithEscapedLineBreaks = json.replace(/\r\n/g, '\\r\\n');
   try {
     return JSON.parse(jsonWithEscapedLineBreaks);
   } catch (exception) {
     failTest('Failed to parse JSON: ' + jsonWithEscapedLineBreaks + ', got ' +
              exception);
   }
 }