Auto merge of #18764 - bradwerth:onlyDPPX, r=heycam

Change MediaExpressionValue::from_css_value to only accept pixels

MozReview-Commit-ID: Hn3twVa8xLo

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1404097
https://reviewboard.mozilla.org/r/184746/

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- [ ] These changes fix #__ (github issue number if applicable).

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components/style/gecko/media_queries.rs

@@ -374,18 +374,8 @@ impl MediaExpressionValue {
                 Some(MediaExpressionValue::BoolInteger(i == 1))
             }
             nsMediaFeature_ValueType::eResolution => {
-                // This is temporarily more complicated to allow Gecko Bug
-                // 1376931 to land. Parts of that bug will supply pixel values
-                // and expect them to be passed through without conversion.
-                // After all parts of that bug have landed, Bug 1404097 will
-                // return this function to once again only allow one type of
-                // value to be accepted: this time, only pixel values.
-                let res = match css_value.mUnit {
-                    nsCSSUnit::eCSSUnit_Pixel => Resolution::Dppx(css_value.float_unchecked()),
-                    nsCSSUnit::eCSSUnit_Inch  => Resolution::Dpi(css_value.float_unchecked()),
-                    _                         => unreachable!(),
-                };
-                Some(MediaExpressionValue::Resolution(res))
+                debug_assert!(css_value.mUnit == nsCSSUnit::eCSSUnit_Pixel);
+                Some(MediaExpressionValue::Resolution(Resolution::Dppx(css_value.float_unchecked())))
             }
             nsMediaFeature_ValueType::eEnumerated => {
                 let value = css_value.integer_unchecked() as i16;