Implement the font-optical-sizing property

[chromium-wpt-export-bot]

Implement the CSS fonts property font-optical-sizing [1]. Typographic
optical sizing means that a font has slight variations in glyph contrast
to better optimize for legibility at different font sizes: The glyph
shapes vary between for example a headline font size and a body text
font size. The CSS font-optical-sizing property with its default value
of auto exists to automatically apply the current font size value to a
variable font's 'opsz' axis. This means, if a variable font supports the
'opsz' axis and optical sizing, the right value is automatically applied
without the need for an explicit font-variation-settings styling.

Intend to implement and ship:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Y3lhEykjfV0

Chromestatus entry:
https://www.chromestatus.com/feature/5685958032752640

[1] https://drafts.csswg.org/css-fonts-4/#font-optical-sizing-def

Bug: 773697
Change-Id: Ifa4b6e042204a3fbf172b8cfe232821d8691283b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1795244
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697197}

[wpt-pr-bot]

Already reviewed downstream.

[drott]

CC @jfkthame - I was trying this test in Firefox release and nightly: In Nightly the font does not get loaded - why might that be? In Release (on Mac) font-variation-settings: 'opsz' <number>; work, but font-optical-sizing: auto; does not seem to get applied. There should be a copy of this test at: http://roettsch.es/variable-opsz.html if you'd like to give it a try. Thanks for taking a look.

[drott]

CC @emilio ^^ is what we discussed here at TPAC, thanks for taking a look!

[emilio]

Poking a bit it seems like the sanitizer is rejecting it:

[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f780a9e0) download completed - font uri: (http://roettsch.es/variabletest_box.ttf) time: 944 ms
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: name: name records are not sorted. (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: Variations: Axis count mismatch (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: Variations: Failed to parse variation region list (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: GDEF: Invalid item variation store (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: GDEF: Failed to parse table (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) downloadable font: rejected by sanitizer (font-family: "variabletest_box" style:normal weight:400 stretch:100 src index:0) source: http://roettsch.es/variabletest_box.ttf
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) [src 0] failed uri: (http://roettsch.es/variabletest_box.ttf) for (variabletest_box) error making platform font
[Child 31282: Main Thread]: D/userfonts userfonts (0x7f62f56460a0) failed all src for (variabletest_box)

But I think we should log a message to the console or so in that case.

[emilio]

Ah, the message goes to the console, but it goes to the "CSS" category, which is disabled by default.

[drott]

Poking a bit it seems like the sanitizer is rejecting it:

Thanks, managed to fix the font to pass OTS, had a wrong name id for the new axis name as well as a missing axis filter entry in the variations store in GDEF. Thanks for the CSS button tip.

[drott]

698b027 should contain the updated font. Thanks for your help @emilio .