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
