webrtc: Fixes WebRtcBrowserTest to use DOM attributes correctly.

chrome/test/data/webrtc/peerconnection.js

Index: chrome/test/data/webrtc/peerconnection.js
diff --git a/chrome/test/data/webrtc/peerconnection.js b/chrome/test/data/webrtc/peerconnection.js
index 96d3c8dac24c416200213b91ef737865bebf0423..78d63cff84cbcdc54b7d7b667c6abdc3d8040abb 100644
--- a/chrome/test/data/webrtc/peerconnection.js
+++ b/chrome/test/data/webrtc/peerconnection.js
@@ -57,7 +57,7 @@ function createLocalOffer(constraints) {
         success_('createOffer');
         setLocalDescription(peerConnection, localOffer);
 
-        returnToTest('ok-' + JSON.stringify(localOffer));
+        returnToTest('ok-' + stringifyDOMObject_(localOffer));
       },
       function(error) { failure_('createOffer', error); },
       constraints);
@@ -89,7 +89,7 @@ function receiveOfferFromPeer(sessionDescJson, constraints) {
       function(answer) {
         success_('createAnswer');
         setLocalDescription(peerConnection, answer);
-        returnToTest('ok-' + JSON.stringify(answer));
+        returnToTest('ok-' + stringifyDOMObject_(answer));
       },
       function(error) { failure_('createAnswer', error); },
       constraints);
@@ -178,7 +178,7 @@ function getAllIceCandidates() {
     return;
   }
 
-  returnToTest(JSON.stringify(gIceCandidates));
+  returnToTest(stringifyDOMObject_(gIceCandidates));
 }
 
 /**
@@ -245,7 +245,7 @@ function success_(method) {
 
 /** @private */
 function failure_(method, error) {
-  throw failTest(method + '() failed: ' + JSON.stringify(error));
+  throw failTest(method + '() failed: ' + stringifyDOMObject_(error));
 }
 
 /** @private */
@@ -280,6 +280,28 @@ function removeStreamCallback_(event) {
 }
 
 /**
+ * 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
  */