ServiceWorker: Add a check if error handler runs on the right thread

content/browser/service_worker/embedded_worker_instance.cc

Index: content/browser/service_worker/embedded_worker_instance.cc
diff --git a/content/browser/service_worker/embedded_worker_instance.cc b/content/browser/service_worker/embedded_worker_instance.cc
index dcf7580597bc687029169a2ba30cc41139c05a63..8a980ef3db305d61eb9b2a993058782769b0a026 100644
--- a/content/browser/service_worker/embedded_worker_instance.cc
+++ b/content/browser/service_worker/embedded_worker_instance.cc
@@ -813,6 +813,11 @@ void EmbeddedWorkerInstance::OnDetached() {
 }
 
 void EmbeddedWorkerInstance::Detach() {
+  // This could be called on the UI thread if |client_| still be valid when the
+  // message loop on the UI thread gets destructed.

[nhiroki, 2016/11/02 07:59:50]

Making an indirection could be saner than directly calling
EmbeddedWorkerInstance's method on an unexpected thread. For example,

namespace {
void CallDetach(EmbeddedWorkerInstance* instance) {
  // This could be...
  if (!BrowserThread::CurrentlyOn(BrowserThread::IO))
    return;
  instance->Detach();
}
}  // namespace

then

client_.set_connection_error_handler(base::Bind(&CallDetach,
base::Unretained(this)));

[horo, 2016/11/02 08:22:54]

+1

+  // TODO(shimazu): Remove this after https://crbug.com/604762 is fixed
+  if (!BrowserThread::CurrentlyOn(BrowserThread::IO))
+    return;

[horo, 2016/11/02 07:49:12]

Please add DCHECK for mojo sw.

if (!BrowserThread::CurrentlyOn(BrowserThread::IO)) {
  DCHECK(ServiceWorkerUtils::IsMojoForServiceWorkerEnabled());
  return;
}

   registry_->DetachWorker(process_id(), embedded_worker_id());
   OnDetached();
 }