servo: Merge #17549 - Make '-moz-context-properties' support 'fill-opacity' and 'stroke-opacity' (from KuoE0:make-moz-context-properties-support-fill-opacity-and-stroke-opacity); r=heycam

Enable 'fill-opacity' and 'stroke-opacity' for '-moz-context-properties' to make the context-{fill|stroke}-opacity work in SVG-as-an-image.

---
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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 [Bug 1373159](https://bugzilla.mozilla.org/show_bug.cgi?id=1373159)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because the test cases will be added in gecko.

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Source-Repo: https://github.com/servo/servo
Source-Revision: 9d1b26de1f24e4183ecf0c8aa4957aec9674d1f9

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 3d0b906c394c8671bf05e3d1f92dcedbf5047da2

servo/components/style/properties/gecko.mako.rs

@@ -4021,6 +4021,10 @@ clip-path
                 self.gecko.mContextPropsBits |= structs::NS_STYLE_CONTEXT_PROPERTY_FILL as u8;
             } else if servo.0 == atom!("stroke") {
                 self.gecko.mContextPropsBits |= structs::NS_STYLE_CONTEXT_PROPERTY_STROKE as u8;
+            } else if servo.0 == atom!("fill-opacity") {
+                self.gecko.mContextPropsBits |= structs::NS_STYLE_CONTEXT_PROPERTY_FILL_OPACITY as u8;
+            } else if servo.0 == atom!("stroke-opacity") {
+                self.gecko.mContextPropsBits |= structs::NS_STYLE_CONTEXT_PROPERTY_STROKE_OPACITY as u8;
             }
             unsafe { gecko.set_raw_from_addrefed::<structs::nsIAtom>(servo.0.into_addrefed()) }
         }