Don't lower priority for scripts inserted by doc.write

HTML Chunks inserted by document.write() are run through a separate
instance of the preload scanner from the main document.  If the main
document scanner has already discovered an image then all scripts
discovered by any preload scanner regardless of where they came from
would be considered late-body.

This behavior causes a regression where a document.write() in the head
that includes multiple script tags will discover them but treat them as
late-body scripts and only load them one at a time.


Cr-Commit-Position: refs/heads/master@{#467029}
16 files changed