Worker: Notify WorkerThread lifecycle events via WorkerReportingProxy
Before this CL, script loading and evaluation are directly notified to
WorkerGlobalScope. After this CL, they are notified via WorkerReportingProxy
that is a proper route.
BUG=
519111,
640843
Committed:
https://crrev.com/ac6098db746f5939263b51863df6f061f0ebdb76
Cr-Commit-Position: refs/heads/master@{#418230}