Selects should scale when rendering while zoomed

Selects should scale when rendering while zoomed
https://bugs.webkit.org/show_bug.cgi?id=147868

Reviewed by Daniel Bates.

When rendering zoomed <select> elements, draw to an image buffer instead of drawing directly
into the context. This allows us to scale the image buffer up before rendering.

* rendering/RenderThemeMac.mm:
(WebCore::RenderThemeMac::paintMenuList): Use ThemeMac::drawCellOrFocusRingWithViewIntoContext
    to render search fields, utilizing an offscreen image buffer only when necessary.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@188399 268f45cc-cd09-0410-ab3c-d52691b4dbfc