[SVGDom] Radial gradient support

Implement support for
https://www.w3.org/TR/SVG/pservers.html#RadialGradients.

BUG=skia:7074

Change-Id: I19645a4a3bbddfd1ee0d08a2775381a0017acbfc
Reviewed-on: https://skia-review.googlesource.com/57340
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 96ef7d6..b5ae1de 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1178,6 +1178,7 @@
       "experimental/svg/model/SkSVGNode.cpp",
       "experimental/svg/model/SkSVGPath.cpp",
       "experimental/svg/model/SkSVGPoly.cpp",
+      "experimental/svg/model/SkSVGRadialGradient.cpp",
       "experimental/svg/model/SkSVGRect.cpp",
       "experimental/svg/model/SkSVGRenderContext.cpp",
       "experimental/svg/model/SkSVGSVG.cpp",