Don't leak a WebServiceWorker when 'current' races with context destruction.

WebServiceWorkerProviderClient::setCurrentServiceWorker passes the
ownership of a WebServiceWorker to the container. If the execution
context is gone, delete the WebServiceWorker instead of dropping it on
the floor.

BUG=363967

Review URL: https://codereview.chromium.org/304023002

git-svn-id: svn://svn.chromium.org/blink/trunk@175023 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerContainer.cpp

@@ -142,8 +142,10 @@ ScriptPromise ServiceWorkerContainer::unregisterServiceWorker(ExecutionContext*
 
 void ServiceWorkerContainer::setCurrentServiceWorker(blink::WebServiceWorker* serviceWorker)
 {
-    if (!executionContext())
+    if (!executionContext()) {
+        delete serviceWorker;
         return;
+    }
     m_current = ServiceWorker::create(executionContext(), adoptPtr(serviceWorker));
 }