Move GuestView code from WebView-specific web_view_iframe.js into

extensions/renderer/resources/guest_view/web_view/web_view_iframe.js

 // Copyright 2015 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.
 
 // This module provides --site-per-process overrides for WebView (<webview>).
 // See web_view.js for details.
 
-var IdGenerator = requireNative('id_generator');
-var WebViewImpl = require('webView').WebViewImpl;
 // NOTE: Do not remove these, we implicitly depend on these in
 // --site-per-process.
 var GuestViewIframe = require('guestViewIframe');
 var GuestViewIframeContainer = require('guestViewIframeContainer');
-
-WebViewImpl.prototype.attachWindow$ = function(opt_guestInstanceId) {
-  // If |opt_guestInstanceId| was provided, then a different existing guest is
-  // being attached to this webview, and the current one will get destroyed.
-  if (opt_guestInstanceId) {
-    if (this.guest.getId() == opt_guestInstanceId) {
-      return true;
-    }
-    this.guest.destroy();
-    this.guest = new GuestView('webview', opt_guestInstanceId);
-  }
-
-  var generatedId = IdGenerator.GetNextId();
-  // Generate an instance id for the container.
-  this.onInternalInstanceId(generatedId);
-  return true;
-};