Give the main frame a RenderWidget.

chrome/browser/ui/webui/print_preview/print_preview_distiller.cc

 // 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.
 
 #include "chrome/browser/ui/webui/print_preview/print_preview_distiller.h"
 
 #include <string>
 
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ skipping 60 matching lines @@
   void CanDownload(const GURL& url,
                    const std::string& request_method,
                    const base::Callback<void(bool)>& callback) override {
     on_failed_callback_.Run();
     // Cancel the download.
     callback.Run(false);
   }
 
   bool ShouldCreateWebContents(
       WebContents* web_contents,
-      int route_id,
-      int main_frame_route_id,
+      int32_t route_id,
+      int32_t main_frame_route_id,
+      int32_t main_frame_widget_route_id,
       WindowContainerType window_container_type,
       const std::string& frame_name,
       const GURL& target_url,
       const std::string& partition_id,
       SessionStorageNamespace* session_storage_namespace) override {
     // Since we don't want to permit child windows that would have a
     // window.opener property, terminate rendering.
     on_failed_callback_.Run();
     // Cancel the popup.
     return false;
@@ skipping 167 matching lines @@
     WebContents* source_web_contents) {
   // TODO(ajwong): Remove the temporary map once prerendering is aware of
   // multiple session storage namespaces per tab.
   content::SessionStorageNamespaceMap session_storage_namespace_map;
   Profile* profile =
       Profile::FromBrowserContext(source_web_contents->GetBrowserContext());
   session_storage_namespace_map[std::string()] = session_storage_namespace;
   return WebContents::CreateWithSessionStorage(
       WebContents::CreateParams(profile), session_storage_namespace_map);
 }