proxy: expand Dialer interface to expose DialContext

[sjpotter]

currently, the Dialer interface returned (from say proxy.SOCKS5()) only exposes the Dial function, while it has a DialContext function as well. As Dial() usage is deprecated, DialContext should be exposed as well.

All implementations in proxy already had a DialContext function besides a single test recording struct, so added a similiar recorder to it.

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[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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Message from Shaya Potter:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/465495.
After addressing review feedback, remember to publish your drafts!