Add regression test for https://crbug.com/1064676

This bug has been fortunately/unexpectedly fixed by:
https://chromium-review.googlesource.com/c/chromium/src/+/2111170

The old code was trying to "guess" the document was the initial empty
document. It failed.

The new code is using CreateCSPForInitialEmptyDocument() to set the CSP
of the initial empty document. It works consistently.

Bug: 1064676
Change-Id: I3778b7a2a0e4eed0599424e3711cbaec24c80c49
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144012
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758793}