ServiceWorker: Print error message when failed to open diskcache

BUG=371675
TEST=n/a
NOTRY=true

Review URL: https://codereview.chromium.org/307503003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272970 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/service_worker/service_worker_storage.cc

@@ -694,7 +694,8 @@ ServiceWorkerDiskCache* ServiceWorkerStorage::disk_cache() {
 
 void ServiceWorkerStorage::OnDiskCacheInitialized(int rv) {
   if (rv != net::OK) {
-    LOG(ERROR) << "Failed to open the serviceworker diskcache.";
+    LOG(ERROR) << "Failed to open the serviceworker diskcache: "
+               << net::ErrorToString(rv);
     // TODO(michaeln): DeleteAndStartOver()
     disk_cache_->Disable();
     state_ = DISABLED;