Worker: Allow dynamic import() on DedicatedWorkerGlobalScope

This CL allows dynamic import() on DedicatedWorkerGlobalScope and adds WPT
tests. Note that ES Modules on DedicatedWorker is an experimental feature behind
the runtime flag.

Design doc:
https://docs.google.com/document/d/1IMGWAK7Wq37mLehwkbysNRBBnhQBo3z2MbYyMkViEnY/edit#heading=h.637avx8i5qtn

Bug: 680046
Change-Id: I1f8fed5c319aab634f96bcfabeb3c95f5dc7d9a7
Reviewed-on: https://chromium-review.googlesource.com/970127
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545748}
18 files changed