This shows up high on the wasted vector capacity logging: 7287 vectors, 585.92KB used of 740.78KB, 154.86KB wasted at: 1 0x1096bbc48 WebCore::StylePropertySet::StylePropertySet(WebCore::CSSProperty const*, int, WebCore::CSSParserMode) 2 0x108da1c5f WebCore::CSSParser::createStyleRule(WTF::Vector<WTF::OwnPtr<WebCore::CSSParserSelector>, 0ul>*) 3 0x108d7748a cssyyparse(void*) 4 0x108d83a7f WebCore::CSSParser::parseSheet(WebCore::StyleSheetInternal*, WTF::String const&, int, WTF::HashMap<WebCore::StyleRule*, WTF::RefPtr<WebCore::CSSRuleSourceData>, WTF::PtrHash<WebCore::StyleRule*>, WTF::HashTraits<WebCore::StyleRule*>, WTF::HashTraits<WTF::RefPtr<WebCore::CSSRuleSourceData> > >*) 5 0x108dbbe43 WebCore::StyleSheetInternal::parseAuthorStyleSheet(WebCore::CachedCSSStyleSheet const*, WebCore::SecurityOrigin const*)
Also being created via: 2531 vectors, 40.50KB used of 158.66KB, 118.16KB wasted at: 1 0x1096bbb80 WebCore::StylePropertySet::StylePropertySet(WebCore::CSSParserMode) 2 0x108f2304b WebCore::ElementAttributeData::updateInlineStyleAvoidingMutation(WebCore::StyledElement*, WTF::String const&) 3 0x1096b6d52 WebCore::StyledElement::parseAttribute(WebCore::Attribute const&) 4 0x109000cdf WebCore::HTMLElement::parseAttribute(WebCore::Attribute const&) 5 0x1096b6b8c WebCore::StyledElement::attributeChanged(WebCore::Attribute const&)
This was fixed by making StylePropertySet a variable-sized object in <http://trac.webkit.org/changeset/118809>