Add support for spreadMethod=reflect and repeat on SVG gradients (for CoreGraphics...

Add support for spreadMethod=reflect and repeat on SVG gradients (for CoreGraphics platforms)
https://bugs.webkit.org/show_bug.cgi?id=5968

Source/WebCore:

Add support for spreadMethod=repeat and reflect. Also, the opacity of a gradient is now
the result of multiplying stop-opacity with the opacity of the color.

Patch by Justin Michaud <justin_michaud@apple.com> on 2018-09-14
Reviewed by Simon Fraser.

Tests: svg/gradients/spreadMethod-expected.svg
       svg/gradients/spreadMethod.svg
       svg/gradients/spreadMethodAlpha-expected.svg
       svg/gradients/spreadMethodAlpha.svg
       svg/gradients/spreadMethodClose0-expected-mismatch.svg
       svg/gradients/spreadMethodClose0.svg
       svg/gradients/spreadMethodClose1-expected-mismatch.svg
       svg/gradients/spreadMethodClose1.svg
       svg/gradients/spreadMethodClose2-expected.svg
       svg/gradients/spreadMethodClose2.svg
       svg/gradients/spreadMethodDiagonal-expected.svg
       svg/gradients/spreadMethodDiagonal.svg
       svg/gradients/spreadMethodDiagonal2-expected.svg
       svg/gradients/spreadMethodDiagonal2.svg
       svg/gradients/spreadMethodDuplicateStop-expected.svg
       svg/gradients/spreadMethodDuplicateStop.svg
       svg/gradients/spreadMethodReversed-expected.svg
       svg/gradients/spreadMethodReversed.svg
       svg/gradients/stopAlpha-expected.svg
       svg/gradients/stopAlpha.svg

* platform/graphics/cg/GradientCG.cpp:
(WebCore::Gradient::paint):
* svg/SVGStopElement.cpp:
(WebCore::SVGStopElement::stopColorIncludingOpacity const):

LayoutTests:

Add new svg tests for linear gradients with spreadMethod, and alpha values specified in
both stop-opacity and color.

Patch by Justin Michaud <justin_michaud@apple.com> on 2018-09-14
Reviewed by Simon Fraser.

* platform/mac/svg/W3C-SVG-1.1/pservers-grad-10-b-expected.png:
* svg/gradients/spreadMethod-expected.svg: Added.
* svg/gradients/spreadMethod.svg: Added.
* svg/gradients/spreadMethodAlpha-expected.svg: Added.
* svg/gradients/spreadMethodAlpha.svg: Added.
* svg/gradients/spreadMethodClose0-expected-mismatch.svg: Added.
* svg/gradients/spreadMethodClose0.svg: Added.
* svg/gradients/spreadMethodClose1-expected-mismatch.svg: Added.
* svg/gradients/spreadMethodClose1.svg: Added.
* svg/gradients/spreadMethodClose2-expected.svg: Added.
* svg/gradients/spreadMethodClose2.svg: Added.
* svg/gradients/spreadMethodDiagonal-expected.svg: Added.
* svg/gradients/spreadMethodDiagonal.svg: Added.
* svg/gradients/spreadMethodDiagonal2-expected.svg: Added.
* svg/gradients/spreadMethodDiagonal2.svg: Added.
* svg/gradients/spreadMethodDuplicateStop-expected.svg: Added.
* svg/gradients/spreadMethodDuplicateStop.svg: Added.
* svg/gradients/spreadMethodReversed-expected.svg: Added.
* svg/gradients/spreadMethodReversed.svg: Added.
* svg/gradients/stopAlpha-expected.svg: Added.
* svg/gradients/stopAlpha.svg: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@236024 268f45cc-cd09-0410-ab3c-d52691b4dbfc