ServiceWorker: check if StopWorker is called twice

content/renderer/service_worker/embedded_worker_dispatcher.cc

Index: content/renderer/service_worker/embedded_worker_dispatcher.cc
diff --git a/content/renderer/service_worker/embedded_worker_dispatcher.cc b/content/renderer/service_worker/embedded_worker_dispatcher.cc
index 2a9251aec82518e319eac0c856911049f5d12653..e68ad202d2f76ce5e016616d9b44bcddf6a7a5a6 100644
--- a/content/renderer/service_worker/embedded_worker_dispatcher.cc
+++ b/content/renderer/service_worker/embedded_worker_dispatcher.cc
@@ -77,7 +77,11 @@ void EmbeddedWorkerDispatcher::OnStartWorker(
 void EmbeddedWorkerDispatcher::OnStopWorker(int embedded_worker_id) {
   TRACE_EVENT0("ServiceWorker", "EmbeddedWorkerDispatcher::OnStopWorker");
   WorkerWrapper* wrapper = workers_.Lookup(embedded_worker_id);
-  DCHECK(wrapper);
+  // OnStopWorker is possible to be called twice.
+  if (!wrapper) {
+    LOG(WARNING) << "Got OnStopWorker for nonexistent worker";
+    return;
+  }
   // This should eventually call WorkerContextDestroyed. (We may need to post
   // a delayed task to forcibly abort the worker context if we find it
   // necessary)