ServiceWorker

69252f38 - Put [SecureContext] to Cache, ServiceWorker, ServiceWorkerRegistration

Put [SecureContext] to Cache, ServiceWorker, ServiceWorkerRegistration Their objects can't be created in non-secure context, but the interface names themselves are exposed in the global object. Also, as they don't intend to provide their states and methods in non-secure contexts, we put the [SecureContext] attribute. Fixes #941.