[SVGDom] Add support for <a> elements

https://www.w3.org/TR/SVG/linking.html#AElement

The Skia SVG DOM is not a user agent, so link semantics are not
particularly interesting.  But since <a> can wrap actual content, it is
important to not drop it on the floor.

The simplest thing to do is turn it into a <g> node and run with it.

Change-Id: I4e103553354746ceb49bc1038680a1c477a1320a
Reviewed-on: https://skia-review.googlesource.com/57620
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed