[ServiceWorker] Add wpt tests to verify Client.type as 'worker'

Currently we have wpt tests verifying Clients.{get,matchAll} can return
clients with type 'window' or 'sharedworker' correctly, this CL adds
support for another type 'worker'.

BUG=705685
TEST=blink_tests

Review-Url: https://codereview.chromium.org/2884843004
Cr-Commit-Position: refs/heads/master@{#474954}
7 files changed