According to the ongoing discussion, import() seems to reject a promise on WorkletGlobalScope. Anyway, let's wait for the consensus.

CL: https://chromium-review.googlesource.com/c/chromium/src/+/790059

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/419d8078283ee3d6f8677c03c18c3e290c7bc2fb

commit 419d8078283ee3d6f8677c03c18c3e290c7bc2fb
Author: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Mon Dec 04 09:30:25 2017

Worklet: Reject dynamic import() on WorkletGlobalScope

All networking APIs including dynamic import() are disallowed on
WorkletGlobalScope. This CL makes dynamic import() always reject a promise with
TypeError[1] on WorkletGlobalScope.

[1] https://github.com/w3c/css-houdini-drafts/issues/506#issuecomment-344488690

Bug:  782538 
Change-Id: Ieb94a4502b0ba35ff9b56e51c8fc34467ab96d0c
Reviewed-on: https://chromium-review.googlesource.com/790059
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521295}
[add] https://crrev.com/419d8078283ee3d6f8677c03c18c3e290c7bc2fb/third_party/WebKit/LayoutTests/http/tests/worklet/dynamic-import-expected.txt
[add] https://crrev.com/419d8078283ee3d6f8677c03c18c3e290c7bc2fb/third_party/WebKit/LayoutTests/http/tests/worklet/dynamic-import.html
[add] https://crrev.com/419d8078283ee3d6f8677c03c18c3e290c7bc2fb/third_party/WebKit/LayoutTests/http/tests/worklet/resources/dynamic-import-worklet-script.js
[modify] https://crrev.com/419d8078283ee3d6f8677c03c18c3e290c7bc2fb/third_party/WebKit/Source/core/dom/WorkletModulatorImpl.cpp
[modify] https://crrev.com/419d8078283ee3d6f8677c03c18c3e290c7bc2fb/third_party/WebKit/Source/core/dom/WorkletModulatorImpl.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f534543c867d6bfdb328761f43d72361ed3d0272

commit f534543c867d6bfdb328761f43d72361ed3d0272
Author: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Tue May 15 08:00:10 2018

Worklet: Remove outdated comment from WPT

Worklets don't support dynamic import (see the issue)

Bug:  782538 
Change-Id: Iea9b4352122e78d1ff671ae09a9947f6a7f1ef3b
TBR: nhiroki@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1058883
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558638}
[modify] https://crrev.com/f534543c867d6bfdb328761f43d72361ed3d0272/third_party/WebKit/LayoutTests/external/wpt/worklets/resources/service-worker-interception-tests.js