Make sure snap_page combined iframe serialized dom

telemetry/third_party/snap-it/content_script.js

 /**
  * Send the neccessary HTMLSerializer properties back to the extension.
  *
  * @param {HTMLSerializer} htmlSerializer The HTMLSerializer.
  */
 function sendHTMLSerializerToExtension(htmlSerializer) {
-  var result = {
-    'html': htmlSerializer.html,
-    'frameHoles': htmlSerializer.frameHoles,
-    'idToStyleIndex': htmlSerializer.idToStyleIndex,
-    'idToStyleMap': htmlSerializer.idToStyleMap,
-    'windowHeight': htmlSerializer.windowHeight,
-    'windowWidth': htmlSerializer.windowWidth,
-    'rootId': htmlSerializer.rootId,
-    'rootStyleIndex': htmlSerializer.rootStyleIndex,
-    'pseudoElementSelectorToCSSMap':
-        htmlSerializer.pseudoElementSelectorToCSSMap,
-    'pseudoElementPlaceHolderIndex':
-        htmlSerializer.pseudoElementPlaceHolderIndex,
-    'pseudoElementTestingStyleIndex':
-        htmlSerializer.pseudoElementStyleTestingIndex,
-    'pseudoElementTestingStyleId': htmlSerializer.pseudoElementTestingStyleId,
-    'unusedId': htmlSerializer.generateId(document),
-    'frameIndex': htmlSerializer.iframeFullyQualifiedName(window)
-  };
-  chrome.runtime.sendMessage(result);
+  chrome.runtime.sendMessage(htmlSerializer.asDict());
 }
 
 var htmlSerializer = new HTMLSerializer();
 htmlSerializer.processDocument(document);
 htmlSerializer.fillHolesAsync(document, sendHTMLSerializerToExtension);