Kind of a big change, to connect several new bits into something useful:
* ID tracking & lookup
* new asPaint() node virtual to support shader (and in the future filter) based paint servers
* <defs>, <linearGradient> and <stop> element support
* 'href', 'offset', 'stop-color', 'stop-opacity' attribute support
* IRI/FuncIRI and rgb(...) parsing
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2327233003
Review-Url: https://codereview.chromium.org/2327233003
The main feature is <svg> viewBox and proper viewport support, but the CL
touches a few other things:
* refactor SkSVGRenderContext to auto-restore canvas state, and split the
presentation bits into a separate CoW SkSVGPresentationContext
* introduce SkSVGNode::onPrepareToRender(), as a way for nodes to push their
custom state before the actual onRender() call (instead of relying on
non-virtual SkSVGNode to know about all possible state bits)
* add a "Type" suffix to SVG types, to disambiguate (e.g. SkSVGRectType vs.
SkSVGRect)
R=robertphillips@google.com,stephana@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2222793002
Review-Url: https://codereview.chromium.org/2222793002
