[document pip] Use the same compatibility mode as the opener
Currently, document picture-in-picture windows use quirks mode by
default, since they're just about:blank windows. This CL makes the pip
document match the opener document's compatibility mode instead.
WICG/document-picture-in-picture#128
https://groups.google.com/a/chromium.org/g/blink-dev/c/IR7qdNj4Zyw
Bug: 370423046
Change-Id: Ib1a84947b2408ae0be236afc2173fbcb0f77b598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5900737
Reviewed-by: Frank Liberato liberato@chromium.org
Commit-Queue: Tommy Steimel steimel@chromium.org
Reviewed-by: Nate Chapin japhet@chromium.org
Cr-Commit-Position: refs/heads/main@{#1363338}