Intent to ship: Unprefixed text-align-last

[Xidorn Quan]

In Firefox 49 I intent to ship unprefixed text-align-last.

It has been shipped prefixed for quite a while, and Chrome has shipped this
property unprefixed since about a year ago [1].

Although CSS Text 3 hasn't entered CR stage, this property is considered
stable. Also it has been widely-used according usage count from Chrome [2],
so breaking change to this property could be risky.

Bug to unprefix: https://bugzilla.mozilla.org/show_bug.cgi?id=1039541
Link to standard:
https://drafts.csswg.org/css-text-3/#text-align-last-property

[1]
https://groups.google.com/a/chromium.org/d/msg/blink-dev/3aLXO38uGI0/t9TtzeZInkMJ
[2] https://www.chromestatus.com/metrics/css/popularity#text-align-last


- Xidorn