Use a Variant instead of a union in CSSSelector

Use a Variant instead of a union in CSSSelector
https://bugs.webkit.org/show_bug.cgi?id=188559

Patch by Alex Christensen <achristensen@webkit.org> on 2018-09-13
Reviewed by Antti Koivisto.

Source/WebCore:

No change in behavior. This just makes some of the existing problems more obvious and easy to fix.

I moved m_caseInsensitiveAttributeValueMatching to RareData because it's only used with RareData.
I only have m_isForPage when assertions are enabled because it's only used for an assertion.
The rest is pretty straightforward translating union syntax to Variant syntax.
I use RefPtr for now where I could use Ref because it's never null to make copying easier, but that's temporary.

* css/CSSSelector.cpp:
(WebCore::CSSSelector::CSSSelector):
(WebCore::CSSSelector::createRareData):
(WebCore::CSSSelector::setAttribute):
(WebCore::CSSSelector::setArgument):
(WebCore::CSSSelector::setLangArgumentList):
(WebCore::CSSSelector::setSelectorList):
(WebCore::CSSSelector::setNth):
(WebCore::CSSSelector::matchNth const):
(WebCore::CSSSelector::nthA const):
(WebCore::CSSSelector::nthB const):
(WebCore::CSSSelector::RareData::RareData):
* css/CSSSelector.h:
(WebCore::CSSSelector::argument const):
(WebCore::CSSSelector::langArgumentList const):
(WebCore::CSSSelector::selectorList const):
(WebCore::CSSSelector::attribute const):
(WebCore::CSSSelector::attributeCanonicalLocalName const):
(WebCore::CSSSelector::setValue):
(WebCore::CSSSelector::CSSSelector):
(WebCore::CSSSelector::~CSSSelector):
(WebCore::CSSSelector::tagQName const):
(WebCore::CSSSelector::tagLowercaseLocalName const):
(WebCore::CSSSelector::value const):
(WebCore::CSSSelector::serializingValue const):
(WebCore::CSSSelector::attributeValueMatchingIsCaseInsensitive const):
(WebCore::CSSSelector::RareData::create): Deleted.
* css/parser/CSSParserImpl.cpp:
(WebCore::CSSParserImpl::parsePageSelector):
* css/parser/CSSParserSelector.h:

Source/WTF:

* wtf/Variant.h:
Add packing macros to make it so Variant-containing structures don't always have 7 bytes of padding per Variant.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@235976 268f45cc-cd09-0410-ab3c-d52691b4dbfc