HtmlAnchorElement members duplicate Uri members

[DartBot]

This issue was originally filed by @seaneagan

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The following members of HtmlAnchorElement all duplicate members of dart:uri's Uri:

hostName
host
hash
pathname
port
protocol
search
origin ???

They ought to be removed, since you can just do:

final uri = new Uri.fromString(anchor.href);
print(uri.scheme);
// etc.

[madsager]

Added Area-DOM, Triaged labels.

[vsmenon]

Not sure it's worth taking this out. It's arguably still convenient to have them on the HtmlAnchorElement. It's also more efficient if you only want one.

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Added AsDesigned label.