Implement Field::SetHidden using Field::SetDisplay.
Implement Field::SetHidden using Field::SetDisplay.

Following up on [1], where the duplicated logic in
Field::SetDisplay was factored out into a helper function,
CL further cleans up a related method: ::SetHidden.

Field::SetHidden(true), for instance, is equivalent
to calling Field::SetDisplay(1), whereas Field::SetHidden(false)
is equivalent to Field::SetDisplay(0);

No behavior change is expected.

[1] https://codereview.chromium.org/2255843002

Review-Url: https://codereview.chromium.org/2266193002

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