Fix flakiness and re-enable FormAutocompleteTest

extensions/renderer/dispatcher.cc

Index: extensions/renderer/dispatcher.cc
diff --git a/extensions/renderer/dispatcher.cc b/extensions/renderer/dispatcher.cc
index 4351b22cc2bff7341a700543ea31b98dc910c69f..c6504e79156631eb8a7e88412d95935cb108a936 100644
--- a/extensions/renderer/dispatcher.cc
+++ b/extensions/renderer/dispatcher.cc
@@ -361,15 +361,19 @@ void Dispatcher::DidCreateDocumentElement(blink::WebFrame* frame) {
                                 .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,