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);
+  if (content_watcher_) {

[not at google - send to devlin, 2015/07/06 16:32:46]

Comment here and below,

// This can happen if the render process has already been shut down.

It's actually puzzling to me that any of this can happen if the render process
has shutdown. Surely that would mean that document elements aren't being
created? In fact is this a testing-only issue?

[kouhei (in TOK), 2015/07/07 00:00:29]

ack
Yes. This is a testing-only issue. Unfortunately browser_tests can run event
loops after content_watcher_ ptr is cleared.

The unjoined HTMLParser thread may post task after OnRenderProcessShutdown is
called for tests, and the tests process message queue again in
RenderViewTest::TearDown().
I couldn't find a clean way to synchronize the parser thread.
PS1 tries to resolve it by synchronizing HTMLParser thread by loadHTML(""), but
I'm not sure which is better.

[not at google - send to devlin, 2015/07/07 19:55:51]

Alright, let's go with what you have and contrary to my previous solution,
mention that this null check is because, in testing, the document lifetime
events can happen after the render process shutdown event. Linking to the bug
would be useful.

[kouhei (in TOK), 2015/07/08 09:23:32]

Done.

+    content_watcher_->DidCreateDocumentElement(frame);
+  }
 }
 
 void Dispatcher::DidMatchCSS(
     blink::WebFrame* frame,
     const blink::WebVector<blink::WebString>& newly_matching_selectors,
     const blink::WebVector<blink::WebString>& stopped_matching_selectors) {
-  content_watcher_->DidMatchCSS(
-      frame, newly_matching_selectors, stopped_matching_selectors);
+  if (content_watcher_) {
+    content_watcher_->DidMatchCSS(
+        frame, newly_matching_selectors, stopped_matching_selectors);
+  }
 }
 
 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