Propagate through documents a flag that represents if any of the
ancestor navigables has a potentially trustworthy origin.
The "potentially trustworthy origin" concept appears to have gotten
confused in a couple of places and we were instead testing if a URL had
"potentially trustworthy" properties.
The main test for the ancestor navigables is
[mixed-content/nested-iframes](https://github.com/web-platform-tests/wpt/blob/master/mixed-content/nested-iframes.window.js)
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- [X] `./mach build -d` does not report any errors
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- [X] These changes fix#36108
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Signed-off-by: Sebastian C <sebsebmc@gmail.com>
