Force enable HTML Imports for CrossSiteDocumentBlockingTest.

This patch is a preparation for Shadow DOM V0, Custom Element V0 (CEv0) and HTML Imports removal.
Since we soon make these APIs only available for test by turning the json5 feature flag
from status: "stable" to status: "test", this patch is a part of it.
(you can see exact flag turning in my WIP patch:
 https://chromium-review.googlesource.com/c/chromium/src/+/1399774)

We should remove/migration the tests using the old APIs.

Bug: 911943
Change-Id: Ieeb6e907aacf86dab153fa49ff4c9ea33fe7da74
Reviewed-on: https://chromium-review.googlesource.com/c/1404765
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Ɓukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622783}
1 file changed