Test calling functions from WorkerContext. Should print multiple SUCCESS lines, followed by DONE.

SUCCESS: postMessage() called directly
SUCCESS: webkitPostMessage() called directly
SUCCESS: postMessage() invoked via postMessage.call()
SUCCESS: webkitPostMessage() invoked via webkitPostMessage.call()
SUCCESS: postMessage() called via intermediate variable
SUCCESS: webkitPostMessage() called via intermediate variable
DONE

