Only accept HTTP and HTTPS urls for opensearch descriptor.

This CL prevents http: or https: urls from referring to file: urls as search descriptor xmls.
Allowing urls to refer to other urls with the same scheme has been considered (e.g. a file: url
referring to an OSDD xml from a file: url), but this currently doesn't work for file: urls
because of http://b/863583, so is not implemented here.

BUG=429838

Review URL: https://codereview.chromium.org/917313004

(cherry picked from commit c4b8fd74e67dfb23ef150c6aa313cb506746f06f)

Cr-Original-Commit-Position: refs/heads/master@{#317723}
Cr-Commit-Position: refs/branch-heads/2311@{#310}
Cr-Branched-From: 09b7de5dd7254947cd4306de907274fa63373d48-refs/heads/master@{#317474}
3 files changed