avoid wrapping named argument name and expression

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2049220?v=3" align="left" width="96" height="96"hspace="10"> Issue by sigmundch
Originally opened as dart-lang/sdk#17836

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We should prefer wrapping arguments, rather than the value of a named argument.

For example, today this:

    main() {
      foo(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, aNamed: parameter);
    }

produces:

    main() {
      foo(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, aNamed:
          parameter);
    }

instead of:
    main() {
      foo(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
          aNamed: parameter);
    }

[DartBot]

<img src="https://avatars.githubusercontent.com/u/8616782?v=3" align="left" width="48" height="48"hspace="10"> Comment by clayberg

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Set owner to @pq.
Added this to the 1.4 milestone.
Removed Type-Defect label.
Added Type-Enhancement label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/17034?v=3" align="left" width="48" height="48"hspace="10"> Comment by kevmoo

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Marked this as blocking #300.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2156198?v=3" align="left" width="48" height="48"hspace="10"> Comment by kasperl

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Removed this from the 1.4 milestone.
Added this to the 1.5 milestone.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2156198?v=3" align="left" width="48" height="48"hspace="10"> Comment by kasperl

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Removed this from the 1.5 milestone.
Added this to the 1.6 milestone.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2156198?v=3" align="left" width="48" height="48"hspace="10"> Comment by kasperl

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Removed this from the 1.6 milestone.
Added Oldschool-Milestone-1.6 label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2156198?v=3" align="left" width="48" height="48"hspace="10"> Comment by kasperl

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Removed Oldschool-Milestone-1.6 label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="48" height="48"hspace="10"> Comment by munificent

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Added AssumedStale label.