Remove unnecessary uses of HTMLDocument

Most of HTMLDocument has already been merged into Document, so these
code paths no longer anything HTMLDocument-specific.

Drive-by:
Remove some unnecessary includes and fix typo in HTMLDocument.cpp

BUG=238368

Review-Url: https://codereview.chromium.org/2197953002
Cr-Commit-Position: refs/heads/master@{#409188}
28 files changed