service worker: Avoid starting up for activation during shutdown

content/browser/service_worker/service_worker_process_manager.cc

Index: content/browser/service_worker/service_worker_process_manager.cc
diff --git a/content/browser/service_worker/service_worker_process_manager.cc b/content/browser/service_worker/service_worker_process_manager.cc
index 74253b59d57f2ec84a059ebaaf58a540e826264d..d59b221bf053b129ba3b92027e664bc633352b02 100644
--- a/content/browser/service_worker/service_worker_process_manager.cc
+++ b/content/browser/service_worker/service_worker_process_manager.cc
@@ -69,7 +69,11 @@ ServiceWorkerProcessManager::~ServiceWorkerProcessManager() {
 
 void ServiceWorkerProcessManager::Shutdown() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  browser_context_ = NULL;
+  {
+    base::AutoLock lock(browser_context_lock_);
+    browser_context_ = nullptr;
+  }
+
   for (std::map<int, ProcessInfo>::const_iterator it = instance_info_.begin();
        it != instance_info_.end();
        ++it) {
@@ -78,6 +82,11 @@ void ServiceWorkerProcessManager::Shutdown() {
   instance_info_.clear();
 }
 
+bool ServiceWorkerProcessManager::IsShutdown() {
+  base::AutoLock lock(browser_context_lock_);
+  return !browser_context_;
+}
+
 void ServiceWorkerProcessManager::AddProcessReferenceToPattern(
     const GURL& pattern, int process_id) {
   if (!BrowserThread::CurrentlyOn(BrowserThread::UI)) {