Auto merge of #16570 - Manishearth:scriptmin-parent, r=heycam

Compute scriptminsize against the parent font base size

It's supposed to be, because it is used in the computation of the font size, so we can't have the current font size as a dependency.

http://searchfox.org/mozilla-central/rev/7aa21f3b531ddee90a353215bd86e97d6974e25b/layout/style/nsRuleNode.cpp#3842

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

@@ -2157,16 +2157,56 @@ ${helpers.single_keyword("-moz-math-variant",
                    internal="True" disable_when_testing="True">
     use app_units::Au;
     use gecko_bindings::structs::NS_MATHML_DEFAULT_SCRIPT_MIN_SIZE_PT;
+    use std::fmt;
+    use style_traits::ToCss;
     use values::HasViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
-    use values::specified::length::{AU_PER_PT, Length};
+    use values::specified::length::{AU_PER_PT, FontBaseSize, NoCalcLength};
 
-    pub type SpecifiedValue = Length;
+    #[derive(Clone, PartialEq, Debug)]
+    pub struct SpecifiedValue(pub NoCalcLength);
 
     pub mod computed_value {
         pub type T = super::Au;
     }
 
+
+    impl ToComputedValue for SpecifiedValue {
+        type ComputedValue = computed_value::T;
+
+        fn to_computed_value(&self, cx: &Context) -> Au {
+            // this value is used in the computation of font-size, so
+            // we use the parent size
+            let base_size = FontBaseSize::InheritedStyle;
+            match self.0 {
+                NoCalcLength::FontRelative(value) => {
+                    value.to_computed_value(cx, base_size)
+                }
+                NoCalcLength::ServoCharacterWidth(value) => {
+                    value.to_computed_value(base_size.resolve(cx))
+                }
+                ref l => {
+                    l.to_computed_value(cx)
+                }
+            }
+        }
+        fn from_computed_value(other: &computed_value::T) -> Self {
+            SpecifiedValue(ToComputedValue::from_computed_value(other))
+        }
+    }
+
+    impl ToCss for SpecifiedValue {
+        fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+            self.0.to_css(dest)
+        }
+    }
+
+    impl HasViewportPercentage for SpecifiedValue {
+        fn has_viewport_percentage(&self) -> bool {
+            self.0.has_viewport_percentage()
+        }
+    }
+
     #[inline]
     pub fn get_initial_value() -> computed_value::T {
         Au((NS_MATHML_DEFAULT_SCRIPT_MIN_SIZE_PT as f32 * AU_PER_PT) as i32)