Auto merge of #13589 - splav:SVGElement#12974, r=pcwalton,Ms2ger

Support SVG element

<!-- Please describe your changes on the following line: -->
minimal SVG element implementation
---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12974 (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/layout/display_list_builder.rs

@@ -1239,7 +1239,8 @@ impl FragmentDisplayListBuilding for Fragment {
             SpecificFragmentInfo::MulticolColumn |
             SpecificFragmentInfo::InlineBlock(_) |
             SpecificFragmentInfo::InlineAbsoluteHypothetical(_) |
-            SpecificFragmentInfo::InlineAbsolute(_) => {
+            SpecificFragmentInfo::InlineAbsolute(_) |
+            SpecificFragmentInfo::Svg(_) => {
                 if opts::get().show_debug_fragment_borders {
                     self.build_debug_borders_around_fragment(state,
                                                              stacking_relative_border_box,