Auto merge of #15226 - dashed:gh-15208, r=emilio

Fix text-overflow serialization.

Fixes https://github.com/servo/servo/issues/15208

- [x] **More tests pending PR review.**
- [x] **Correct placement of unit test**

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #15208 (github issue number if applicable).

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15226)
<!-- Reviewable:end -->

components/style/properties/longhand/text.mako.rs

@@ -18,6 +18,7 @@
     use style_traits::ToCss;
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
+    use cssparser;
 
     impl ComputedValueAsSpecified for SpecifiedValue {}
     impl NoViewportPercentage for SpecifiedValue {}
@@ -75,7 +76,9 @@
             match *self {
                 Side::Clip => dest.write_str("clip"),
                 Side::Ellipsis => dest.write_str("ellipsis"),
-                Side::String(ref s) => dest.write_str(s)
+                Side::String(ref s) => {
+                    cssparser::serialize_string(s, dest)
+                }
             }
         }
     }