Removing meta tag and name attribute should re-evaluate theme-color.

The algorithm for selecting the theme-color should be re-run in these
cases according to [1].

Also, this prepares for the same behavior required for the color-scheme
meta.

[1] https://html.spec.whatwg.org/multipage/semantics.html#meta-theme-color

Bug: 960734, 925935
Change-Id: I1529e3540cbc8df6035fb820e67fcbd7797fa63e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1601141
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658064}
4 files changed