ServiceWorker

86d94149 - Make Client.postMessage to unloaded client not throw (#1293)

Make Client.postMessage to unloaded client not throw (#1293) https://github.com/w3c/ServiceWorker/commit/cf834f052bc0aed0795fbf29cbf1c6f251dd5c9d clarified the target object can be null, and it must throw in that case. But https://github.com/w3c/ServiceWorker/issues/1291 pointed out that we cannot implement that behavior without blocking the service worker process in multi-process browser architectures. This change makes the control return right away if the target client has been unloaded. Fixes #1291.