Link rel=modulepreload: Support integrity attribute

This CL enables subresource integrity check for link rel=modulepreload, by
passing integrity value to ScriptFetchOptions.

Note that this is only for modulepreload; integrity is still not supported
for link rel=preload (crbug.com/677022).

Bug: 740886
Change-Id: I09159ed802e49b402e71ff464dee56a380a73b07
Reviewed-on: https://chromium-review.googlesource.com/773719
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518037}
9 files changed