[SVGDom] Initial <pattern> support

https://www.w3.org/TR/SVG/pservers.html#Patterns

Change-Id: I80455c4ae04cf03526f8e8797f40b0b2d24e043f
Reviewed-on: https://skia-review.googlesource.com/58461
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 66ea0d8..0d99236 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1177,6 +1177,7 @@
       "experimental/svg/model/SkSVGLinearGradient.cpp",
       "experimental/svg/model/SkSVGNode.cpp",
       "experimental/svg/model/SkSVGPath.cpp",
+      "experimental/svg/model/SkSVGPattern.cpp",
       "experimental/svg/model/SkSVGPoly.cpp",
       "experimental/svg/model/SkSVGRadialGradient.cpp",
       "experimental/svg/model/SkSVGRect.cpp",