select: Don't touch dimensions of DOM elements if not necesary

[narqo]

Both access to CSS min-width and DOM offsetWidth trigger Layout and Paint events in browsers. This may lead to unexpected delays during selects' initialisation.

With this changes dimensions are touched only before menu block is going to become visible or if button's width was potentially changed.

/cc @dfilatov

[dfilatov]

Could you add some numbers showing something?

[narqo]

Could you add some numbers showing something

Sure 600 and 1200. Just kidding :))

Here are two pages with 30 selects:

• http://narqo.github.io/bem-components-bench/benchs/v2/select.html (current bem-components#v2)
• http://narqo.github.io/bem-components-bench/benchs/next/select.html (version with this fixes)

Click on the "Очистить" button leads to synchronous initialisation of all selects via this.findBlocksInside('select'). See the code

As we have a lot of "Forced synchronous layout" calls during onSetMod → js → inited processing in selects in v2 version now, the freeze during initialisation can reach 1200ms on the mobile devices (checked with iPhone 4s).

[dfilatov]

👍