Restrict the main and subresources SXGs to be served from the same origin

To limit the complexity, we are restricting the main SXG and the
subresources SXGs to be served from the same origin.

https://github.com/WICG/webpackage/issues/347#issuecomment-455494121

Bug: 935267
Change-Id: I7cf85a1a23a5b0490da45fb39fd88e66108ed633
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621482
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661631}
3 files changed