Fix potential crash causes in ServiceWorker LayoutTests

Source/modules/serviceworkers/ServiceWorkerError.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 #include "ServiceWorkerError.h"
 
 using blink::WebServiceWorkerError;
 namespace WebCore {
 
 String ServiceWorkerError::errorString(WebServiceWorkerError::ErrorType type)
 {
     switch (type) {
     case WebServiceWorkerError::DisabledError:
         return "DisabledError";
-    default:
-        ASSERT_NOT_REACHED();
+    case WebServiceWorkerError::SecurityError:
+        return "SecurityError";
+    case WebServiceWorkerError::InstallError:
+        return "InstallError";
+    case WebServiceWorkerError::ActivateError:
+        return "ActivateError";
+    case WebServiceWorkerError::UnknownError:
+        return "UnknownError";
     }
+    ASSERT_NOT_REACHED();
     return String();
 }
 
 }