Fix flakiness and re-enable FormAutocompleteTest

extensions/renderer/dispatcher.cc

 // Copyright 2014 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 "extensions/renderer/dispatcher.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/alias.h"
@@ skipping 343 matching lines @@
   // using Chrome styles, then insert the Chrome extension stylesheet.
   if (extension && extension->is_extension() &&
       OptionsPageInfo::ShouldUseChromeStyle(extension) &&
       effective_document_url == OptionsPageInfo::GetOptionsPage(extension)) {
     frame->document().insertStyleSheet(
         WebString::fromUTF8(ResourceBundle::GetSharedInstance()
                                 .GetRawDataResource(IDR_EXTENSION_CSS)
                                 .as_string()));
   }
 
-  content_watcher_->DidCreateDocumentElement(frame);
+  // In testing, the document lifetime events can happen after the render
+  // process shutdown event.
+  // See: http://crbug.com/21508 and http://crbug.com/500851
+  if (content_watcher_) {
+    content_watcher_->DidCreateDocumentElement(frame);
+  }
 }
 
 void Dispatcher::OnExtensionResponse(int request_id,
                                      bool success,
                                      const base::ListValue& response,
                                      const std::string& error) {
   request_sender_->HandleResponse(request_id, success, response, error);
 }
 
 void Dispatcher::DispatchEvent(const std::string& extension_id,
@@ skipping 1059 matching lines @@
   // The "guestViewDeny" module must always be loaded last. It registers
   // error-providing custom elements for the GuestView types that are not
   // available, and thus all of those types must have been checked and loaded
   // (or not loaded) beforehand.
   if (context_type == Feature::BLESSED_EXTENSION_CONTEXT) {
     module_system->Require("guestViewDeny");
   }
 }
 
 }  // namespace extensions