Intent to ship: CSS text-justify property

[Jeremy Chen]

After Bug 276079 <https://bugzilla.mozilla.org/show_bug.cgi?id=276079> is
landed, I intent to turn CSS text-justify property on by default on all
platforms in Bug 1343512
<https://bugzilla.mozilla.org/show_bug.cgi?id=1343512>. It has been
developed behind the layout.css.text-justify.enabled preference.

Summary: This property selects the justification method used when a line’s
alignment is set to justify, i.e., text-align: justify, text-align-last:
justify.

Status in other browsers [1]:
Currently, the values specified by spec. are

auto | none | inter-word | inter-character

plus distribute as a legacy alias for inter-character.

*IE & Edge*
Supports inter-word, but not inter-character or none. Also supports the
following unofficial values: distribute , distribute-all-lines,
distribute-center-last, inter-cluster, inter-ideograph, newspaper.

*Blink*
inter-word and distribute values are supported behind the "Experimental
platform features" flag.
Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=248894

*WebKit*
According to caniuse [1], WebKit doesn't support any of these values yet.
Bug: https://bugs.webkit.org/show_bug.cgi?id=99945

This feature was previously discussed in this "intent to implement" thread:
https://groups.google.com/forum/#!searchin/mozilla.dev.
platform/text-justify%7Csort:relevance/mozilla.dev.platform/I00tLlnmTYk/
Tz8wcRTJBAAJ
<https://groups.google.com/forum/#%21searchin/mozilla.dev.platform/text-justify%7Csort:relevance/mozilla.dev.platform/I00tLlnmTYk/Tz8wcRTJBAAJ>

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cg
i?id=1343512 <https://bugzilla.mozilla.org/show_bug.cgi?id=1343512>

Link to standard: https://drafts.csswg.org/css-text-3/#text-justify-property
AFAIK, CSS Text Module Level 3 is listed as an upcoming CR [2], so the
spec. is stable enough.

Target release:
Since we are in the late Firefox 54, I'd prefer let text-justify ride the
train in Firefox 55 (next Nightly).


[1] http://caniuse.com/#search=text-justify
[2] https://wiki.mozilla.org/CSS#Upcoming_CRs

-Jeremy Chen