Don't create ServiceWorker provider in dedicated workers (yet)
Don't create ServiceWorker provider in dedicated workers (yet)

We don't expose ServiceWorker in WorkerNavigator yet, and creating
a provider for workers could cause data-race with the current code.
(See https://code.google.com/p/chromium/issues/detail?id=423107#c8 for
more details)

BUG=423107,371690
R=michaeln

Review URL: https://codereview.chromium.org/717553003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@185090 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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