Convert fast/multicol/single-line into a reftest.

Convert fast/multicol/single-line into a reftest.

Based on work by andersr.

Removed column-rule and column-gap to make the ref simple.

Also removed related (but useless) test in newmulticol/.

Added   in front of some text to avoid irrelevant minor differences. The
font (or font engine) used in Linux appears to have (or cause) a tiny negative
left bearing for the "N" glyph, so it will overflow the box by half a pixel or
even less. The difference between multicol and non-multicol is that multicol
rendering always sets a clip rectangle for each column, while non-multicol
doesn't do this. In fact, non-multicol rendering won't even set a clip
rectangle if you specify overflow:hidden - unless we actually detect that
there's content that would overflow (if the calculated bounding box isn't fully
contained by the padding box). In this case, from the rendering code's point of
view, we're only painting simple text inside the bounds of the content box, so
it won't realize that there's a tiny amount of overflow caused by the font.

BUG=386567
R=andersr@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=188523

[andersr, 2015-01-16 09:48:06]

> Added   in front of some text to avoid irrelevant minor differences [...]

Aha!

lgtm

[mstensho (USE GERRIT), 2015-01-16 09:52:09]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-01-16 09:53:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/825593003/1

[commit-bot: I haz the power, 2015-01-16 09:56:55]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=188523