Clone service worker objects to nested workers

Bug: 31666
Change-Id: I8db30dee7c6b72430eb4083536fca73606de76e8
Reviewed-on: https://chromium-review.googlesource.com/1130101
Commit-Queue: Nate Chapin <japhet@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574707}
9 files changed