Reviewed by Dave Hyatt.

        Implement repeating CSS3 gradients
        https://bugs.webkit.org/show_bug.cgi?id=51843

        Add support for repeating gradients, via the new gradient functions
        -webkit-repeating-linear-gradient and -webkit-repeating-radial-gradient.

        Tests: fast/gradients/css3-repeating-linear-gradients.html
               fast/gradients/css3-repeating-radial-gradients.html

        * css/CSSGradientValue.h:
        (WebCore::CSSGradientValue::isRepeating): Accessor for whethe the gradient repeats.
        (WebCore::CSSGradientValue::CSSGradientValue): Pass CSSGradientRepeat in.
        (WebCore::CSSLinearGradientValue::create): Pass CSSGradientRepeat.
        (WebCore::CSSLinearGradientValue::CSSLinearGradientValue): Ditto
        (WebCore::CSSRadialGradientValue::create): Ditto.
        (WebCore::CSSRadialGradientValue::CSSRadialGradientValue): Ditto.

        * css/CSSGradientValue.cpp:
        (WebCore::CSSGradientValue::addStops): Pass maxLengthForRepeat, which
        is used for repeating radial gradients. Add code to repeat the stops,
        adding stops before the start, and after the end until the 0-N range is
        covered, where N is large enough to ensure the box is covered. Fix an issue
        with repeating gradients where if both stops were < 0, it would fail to clamp
        them to 0.

        (WebCore::CSSLinearGradientValue::cssText): Output strings for repeating gradients.
        (WebCore::CSSLinearGradientValue::createGradient): maxExtent for linear gradients is 1,
        because they are guaranteed to fill the box already.
        (WebCore::CSSRadialGradientValue::cssText): Output strings for repeating gradients.
        (WebCore::CSSRadialGradientValue::createGradient): Compute the distance to the furthest
        corner in order to inform addStops() how much additional extent is required.

        * css/CSSParser.cpp:
        (WebCore::CSSParser::parseDeprecatedGradient): Old gradients never repeat.
        (WebCore::CSSParser::parseLinearGradient): Pass down CSSGradientRepeat.
        (WebCore::CSSParser::parseRadialGradient): Ditto.
        (WebCore::CSSParser::isGeneratedImageValue): Add repeating gradient functions.
        (WebCore::CSSParser::parseGeneratedImage): Ditto.
        * css/CSSParser.h: Pass CSSGradientRepeat to gradient functions.
        * platform/graphics/cg/GradientCG.cpp: Remove unused #include.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@75097 268f45cc-cd09-0410-ab3c-d52691b4dbfc