Reviewed by Dave Hyatt.

https://bugs.webkit.org/show_bug.cgi?id=52370
<rdar://problem/8856808>
Style sharing optimization no longer works on major web sites
        
The code in CSSStyleSelector::locateSharedStyle() that tries to share style information between element has been defeated 
by widespread use of certain CSS selectors (:first-child pseudo class and similar). The current implementation disables
the sharing optimization for the whole page if one of these constructs is seen in any style sheet used by the page.  
        
This patch gets the style sharing back to 25-40% range on most web sites.

* css/CSSMutableStyleDeclaration.h:
(WebCore::CSSMutableStyleDeclaration::propertiesEqual):
            
    Needed to improve equality checking in NamedNodeMap::mappedMapsEquivalent.
        
* css/CSSSelector.h:
(WebCore::CSSSelector::isSiblingSelector):
        
    Test for selectors that are affected by the sibling elements.
        
* css/CSSStyleSelector.cpp:
(WebCore::elementCanUseSimpleDefaultStyle):
(WebCore::collectSiblingRulesInDefaultStyle):
(WebCore::assertNoSiblingRulesInDefaultStyle):
            
    Extract sibling rules from the MathML default stylesheet. 
    Assert that no other default stylesheet has them.
            
(WebCore::CSSStyleSelector::CSSStyleSelector):
(WebCore::CSSStyleSelector::locateCousinList):
(WebCore::CSSStyleSelector::matchesSiblingRules):
(WebCore::CSSStyleSelector::canShareStyleWithElement):
(WebCore::CSSStyleSelector::locateSharedStyle):
(WebCore::CSSStyleSelector::styleForElement):
(WebCore::collectIdsAndSiblingRulesFromList):
(WebCore::CSSRuleSet::collectIdsAndSiblingRules):

    Track sibling rules and ids used in the stylesheets to allow much more fine-grained rejection of cases
    where style sharing can't be used.

* css/CSSStyleSelector.h:
* dom/NamedNodeMap.cpp:
(WebCore::NamedNodeMap::mappedMapsEquivalent):
            
    Check also for CSSValue mutation from DOM. 
            
* mathml/MathMLMathElement.cpp:
(WebCore::MathMLMathElement::insertedIntoDocument):
* mathml/MathMLMathElement.h:
        
    MathML default style sheet has sibling rules which don't get noticed by the normal document
    stylesheet parsing.
        
* rendering/style/RenderStyle.h:
(WebCore::InheritedFlags::setFirstChildState):
(WebCore::InheritedFlags::setLastChildState):
(WebCore::InheritedFlags::setChildIndex):
        
    These all make style non-shareable (unique).

LayoutTests: https://bugs.webkit.org/show_bug.cgi?id=52370
Style sharing optimization no longer works on major web sites
        
Reviewed by Dave Hyatt.

These are progressions (with no noticable visual change). 
MathML code was improperly sharing style.

* platform/mac/mathml/presentation/fractions-vertical-alignment-expected.txt:
* platform/mac/mathml/presentation/subsup-expected.txt:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76012 268f45cc-cd09-0410-ab3c-d52691b4dbfc