A partial fix for http://bugs.webkit.org/show_bug.cgi?id=13021
        XPath can be very slow

        * xml/XPathExpression.cpp:
        (WebCore::XPathExpression::evaluate): Cache evaluationContext in a local variable.

        * xml/XPathExpressionNode.cpp:
        (WebCore::XPath::Expression::evaluationContext):
        * xml/XPathExpressionNode.h:
        (WebCore::XPath::Expression::addSubExpression):
        (WebCore::XPath::Expression::subExprCount):
        (WebCore::XPath::Expression::subExpr):
        * xml/XPathFunctions.cpp:
        * xml/XPathFunctions.h:
        (WebCore::XPath::Function::setName):
        (WebCore::XPath::Function::arg):
        (WebCore::XPath::Function::argCount):
        (WebCore::XPath::Function::name):
        Made one-liners critical for performance inline.

        * xml/XPathGrammar.y: Fully parse NodeTests, so that strings are no longer passed for what is
        essentially an enum. Use LocationPath accessors to add steps, instead of directly manipulating
        internal data members.

        * xml/XPathParser.cpp:
        (WebCore::XPath::Parser::parseStatement):
        (WebCore::XPath::Parser::registerNodeTest):
        (WebCore::XPath::Parser::deleteNodeTest):
        * xml/XPathParser.h:
        Added support methods for changes in XPathGrammar.y.

        * xml/XPathPath.cpp:
        (WebCore::XPath::Filter::evaluate): Cache evaluationContext in a local variable. Use swap() to avoid
        performing vector assignments.
        (WebCore::XPath::LocationPath::evaluate): Use swap() to avoid performing vector assignments.
        (WebCore::XPath::LocationPath::optimizeStepPair): This new method is called during LocationPath construction, 
        to simplify the path as it's being built. Currently, the only optimized case is "//*" - it is a basis for
        important operations that cannot be efficiently written in XPath 1.0, but can be optimized with a little bit
        of XPath 2.0.
        (WebCore::XPath::LocationPath::appendStep): A new accessor that modifies m_steps and calls optimizeStepPair().
        (WebCore::XPath::LocationPath::insertFirstStep): Ditto.
        * xml/XPathPath.h:
        (WebCore::XPath::LocationPath::setAbsolute): A new accessor.

        * xml/XPathStep.h:
        (WebCore::XPath::Step::NodeTest::):
        (WebCore::XPath::Step::NodeTest::NodeTest):
        (WebCore::XPath::Step::NodeTest::kind):
        (WebCore::XPath::Step::NodeTest::data):
        Step::NodeTest is a new sub-class that represents a fully parsed NodeTest.
        (WebCore::XPath::Step::axis):
        (WebCore::XPath::Step::nodeTest):
        (WebCore::XPath::Step::nodeTestData):
        (WebCore::XPath::Step::namespaceURI):
        (WebCore::XPath::Step::predicates):
        (WebCore::XPath::Step::setAxis):
        (WebCore::XPath::Step::setNodeTest):
        (WebCore::XPath::Step::setNodeTestData):
        (WebCore::XPath::Step::setNamespaceURI):
        (WebCore::XPath::Step::setPredicates):
        New accessors that let optimizeStepPair() manipulate Step data.

        * xml/XPathStep.cpp:
        (WebCore::XPath::Step::Step): Use the new NodeTest class.
        (WebCore::XPath::Step::evaluate): Cache evaluationContext in a local variable. Use swap() to avoid
        performing unneeded vector assignments.
        (WebCore::XPath::Step::nodesInAxis): Cosmetic changes.
        (WebCore::XPath::Step::nodeTestMatches): Use NodeTest instead of parsing the test from string each time.
        Added a partial implementation of XPath 2.0 element() node test.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20102 268f45cc-cd09-0410-ab3c-d52691b4dbfc