Add WorkerGlobalScope* param to WorkerReportingProxy::workerGlobalScopeStarted

To make ServiceWorker wiring slightly easier.
(This method is currently used only by ServiceWorker)

BUG=313530

Review URL: https://codereview.chromium.org/137633004

git-svn-id: svn://svn.chromium.org/blink/trunk@165404 bbb929c8-8fbe-4397-9dbb-9b2b20218538