This patch ensures each HTML page has a DOCTYPE (to trigger
standards mode as opposed to quirks mode), a <meta
charset="utf-8">, and a <title>.

Additionally, it removes redundant attribute/value pairs such
as `type="text/javascript"` on <script> elements or
`type="text/css"` on <style> or <link rel="stylesheet">
elements. [1]

Finally, it removes the optional solidus for self-closing HTML
elements. [2]

[1] https://mathiasbynens.be/notes/html5-levels#type-attributes
[2] https://mathiasbynens.be/notes/html5-levels#solidus

Change-Id: I66d2700be120dc8fd52bdf38f9d34749f55e1e7f
Reviewed-on: https://chromium-review.googlesource.com/c/1396084Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58561}