Change [Global=ServiceWorker] to [Global=Worker&ServiceWorker] in ServiceWorkerGlobalScope.idl

ServiceWorker should see everything in Worker, just as DedicatedWorker and
SharedWorker already do, per Kinuko:
https://code.google.com/p/chromium/issues/detail?id=369115#c3
http://heycam.github.io/webidl/#Global

R=kinuko
TBR=haraken
BUG=369115

Review URL: https://codereview.chromium.org/277853002

git-svn-id: svn://svn.chromium.org/blink/trunk@173732 bbb929c8-8fbe-4397-9dbb-9b2b20218538