Spin button in input[type=number] should not ignore paddings.

Spin button in input[type=number] should not ignore paddings.

The old behavior was to emulate Windows spin button appearance. Now
we don't use Windows-native controls and don't need to emulate it.

Implementation:
This CL removes special layout code for spin buttons in RenderTextControlSingleLine,
and the spin button layout relies on CSS flexible box.
As for Mac, we can't stretch NSStepper to arbitrary sizes. We need to
apply align-item:center. Also, adjust control size threshold because
spin buttons need to fit into the font height.

Test:
* We need to do rebaseline for some layout tests.
* This CL removes fast/forms/number/number-large-padding.html,
  which made sense for the special layout.
* Add font-size to number-spinbutton-in-multi-column.html
  because OSX spin button height depends on font size, and we don't
  stretch it.

BUG=128957, 330117, 356939
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=171315

[tkent, 2014-04-10 03:04:48]

Keishi, would you review this please?

[keishi, 2014-04-11 05:02:43]

lgtm

[tkent, 2014-04-11 05:09:23]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2014-04-11 05:09:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/230193002/60001

[commit-bot: I haz the power, 2014-04-11 05:24:43]

Change committed as 171315