Properties that take <position> should not accept 3 values

[Eric Willigers]

https://drafts.csswg.org/css-images-3/#the-object-position
The relevant syntax is

<position> = [
  [ left | center | right ] || [ top | center | bottom ]
|
  [ left | center | right | <length-percentage> ]
  [ top | center | bottom | <length-percentage> ]?
|
  [ [ left | right ] <length-percentage> ] &&
  [ [ top | bottom ] <length-percentage> ]
]

A number of test cases currently fail:
https://wpt.fyi/results/css/css-images/parsing/object-position-invalid.html

e.g. "center left 1px" should not be accepted.

This also applies to <position> in gradients

[Radar WebKit Bug Importer]

<rdar://problem/44110851>

[Simon Fraser (smfr)]

Seems like some css/css-shapes tests are still expecting the 3-value syntax.

[Simon Fraser (smfr)]

Created attachment 381985 [details]
Patch

[Simon Fraser (smfr)]

*** Bug 200213 has been marked as a duplicate of this bug. ***

[Simon Fraser (smfr)]

Created attachment 381988 [details]
Patch

[Antti Koivisto]

Comment on attachment 381988 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=381988&action=review

> Source/WebCore/css/parser/CSSPropertyParserHelpers.cpp:926
> +        if (values[i + 1] && !values[i + 1]->isValueID())

Relying on caller to ensure i + 1 is not out of bounds is not very nice. How about passing values as std::array or something?

[Simon Fraser (smfr)]

https://trac.webkit.org/r251668

[Simon Fraser (smfr)]

*** Bug 148211 has been marked as a duplicate of this bug. ***