Don't sniff file URLs for HTML.

If a file with an extension other than html / htm is downloaded, and
Chrome was used to open the file, it could sniff it as being HTML,
which seems unexpected.

The new logic is not applied to WebView, as existing consumers may
depend on the legacy behavior.

Bug: 777737
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: Iaa72004a3a8de2df99f154c95014e4f6351ce532
Reviewed-on: https://chromium-review.googlesource.com/853036
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Reviewed-by: Daichi Hirono <hirono@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533429}
19 files changed