Move GuestView code from WebView-specific web_view_iframe.js into

extensions/renderer/resources/guest_view/guest_view_iframe_container.js

Index: extensions/renderer/resources/guest_view/guest_view_iframe_container.js
diff --git a/extensions/renderer/resources/guest_view/guest_view_iframe_container.js b/extensions/renderer/resources/guest_view/guest_view_iframe_container.js
index 3f1c5d9d42d8d4cb673234aa4b867c1f79191930..4cb27afa4c1a2ba150bf9a1fd564b1b0f62ae646 100644
--- a/extensions/renderer/resources/guest_view/guest_view_iframe_container.js
+++ b/extensions/renderer/resources/guest_view/guest_view_iframe_container.js
@@ -5,6 +5,7 @@
 // --site-per-process overrides for guest_view_container.js
 
 var GuestViewContainer = require('guestViewContainer').GuestViewContainer;
+var IdGenerator = requireNative('id_generator');
 
 GuestViewContainer.prototype.createInternalElement$ = function() {
   var iframeElement = document.createElement('iframe');
@@ -13,3 +14,10 @@ GuestViewContainer.prototype.createInternalElement$ = function() {
   privates(iframeElement).internal = this;
   return iframeElement;
 };
+
+GuestViewContainer.prototype.attachWindow$ = function() {
+  var generatedId = IdGenerator.GetNextId();
+  // Generate an instance id for the container.
+  this.onInternalInstanceId(generatedId);
+  return true;
+};