servo: Merge #17455 - Implement webkit prefixed values for display property (from canaltinova:webkit-displays); r=Manishearth

Added -webkit-{flex,inline-flex} values as flex, inline-flex. I didn't do this gecko only since that doesn't require anything in layout side.

---
<!-- 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 #15400 (github issue number if applicable).

Source-Repo: https://github.com/servo/servo
Source-Revision: dfc44a0d35a1905247cddb926c99e87000b96b59

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : e20dd65442b564267626bf5e4827821619efb4bc

servo/components/style/properties/longhand/box.mako.rs

@@ -19,9 +19,10 @@
         values = """inline block inline-block
             table inline-table table-row-group table-header-group table-footer-group
             table-row table-column-group table-column table-cell table-caption
-            list-item flex inline-flex
-            none
+            list-item none
         """.split()
+        webkit_prefixed_values = "flex inline-flex".split()
+        values += webkit_prefixed_values
         if product == "gecko":
             values += """grid inline-grid ruby ruby-base ruby-base-container
                 ruby-text ruby-text-container contents flow-root -webkit-box
@@ -121,6 +122,11 @@
                     Ok(computed_value::T::${to_rust_ident(value)})
                 },
             % endfor
+            % for value in webkit_prefixed_values:
+                "-webkit-${value}" => {
+                    Ok(computed_value::T::${to_rust_ident(value)})
+                },
+            % endfor
         }
     }