[trusted types] Support reporting and report-only mode.

Bug: 739170
Change-Id: I7c1e4db4f22166692d9fdd90c60d2ef61635033b
Reviewed-on: https://chromium-review.googlesource.com/c/1456012


Commit-Queue: Daniel Vogelheim <vogelheim@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Andy Paicu <andypaicu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634145}