For some specific cases (one of them see below) where are requirement to
identify the reason of the attribute mutation (by whom/why it was
changed - by cloning, parser or directly), so the following `reason`
parameter was added to `AttributeMutation::Set` option.
Note that for the HTMLMediaElement the internal `muted` state should be
set to true when the element is created and the element has a `muted`
content attribute specified (should be done once on the first attribute
mutation caused by parser or cloning).
See https://html.spec.whatwg.org/multipage/#dom-media-muted
Testing: Improvements in the following tests
-
html/semantics/embedded-content/media-elements/user-interface/muted.html
Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>
