meta charset and meta equiv="Content-Type" seem unable to switch away from UTF-8

[pshaughn]

WPT test html/semantics/scripting-1/the-script-element/script-charset-02 tests out various things that the <meta charset=> tag should do, and none of them are happening. Charsets do exist and can be selected other ways, but the meta tag isn't doing it in this test.

[pshaughn]

It looks like every WPT test in html/syntax that tries to get to a non-utf8 charset via a meta tag, either charset or http-equiv, fails by staying in utf8.

• html/syntax/parsing-html-fragments/the-input-byte-stream-007.html
• html/syntax/parsing-html-fragments/the-input-byte-stream-009.html
• html/syntax/parsing-html-fragments/the-input-byte-stream-030.html
• html/syntax/parsing/meta-inhead-insertion-mode.html
• html/syntax/parsing/quotes-in-meta.html

[pshaughn]

Since this needs to happen very early during parsing, and not via DOM, it is probably not dependent on whether http-equiv is commented out in the IDL; charset isn't even in the IDL and is supposed to work.

[jdm]

This is related to #6414.