net/http: allocate CloseNotifier channel lazily

[das7pad]

The CloseNotifier interface is deprecated. We can defer allocating the
backing channel until the first use of CloseNotifier.

goos: linux
goarch: amd64
pkg: net/http
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
                   │   before    │               after                │
                   │   sec/op    │   sec/op     vs base               │
Server-8             160.8µ ± 2%   160.1µ ± 1%       ~ (p=0.353 n=10)
CloseNotifier/h1-8   222.1µ ± 4%   226.4µ ± 7%       ~ (p=0.143 n=10)
geomean              189.0µ        190.4µ       +0.75%

                   │    before    │                after                │
                   │     B/op     │     B/op      vs base               │
Server-8             2.292Ki ± 0%   2.199Ki ± 0%  -4.07% (p=0.000 n=10)
CloseNotifier/h1-8   3.224Ki ± 0%   3.241Ki ± 0%  +0.51% (p=0.000 n=10)
geomean              2.718Ki        2.669Ki       -1.80%

                   │   before   │                after                │
                   │ allocs/op  │ allocs/op   vs base                 │
Server-8             21.00 ± 0%   20.00 ± 0%  -4.76% (p=0.000 n=10)
CloseNotifier/h1-8   50.00 ± 0%   50.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean              32.40        31.62       -2.41%
¹ all samples are equal

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Jakob Ackermann:

Patch Set 1:

(1 comment)

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