Add glue for calc values

ports/geckolib/gecko_bindings/sugar/mod.rs

@@ -3,4 +3,5 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 mod ns_style_auto_array;
+mod ns_style_coord;
 mod ns_t_array;

ports/geckolib/gecko_bindings/sugar/ns_style_coord.rs

@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use structs::{nsStyleCoord_CalcValue, nsStyleCoord_Calc, nsStyleUnit, nsStyleUnion};
+use bindings::{Gecko_ResetStyleCoord, Gecko_SetStyleCoordCalcValue};
+
+// Functions here are unsafe because it is possible to use the wrong nsStyleUnit
+// FIXME we should be pairing up nsStyleUnion and nsStyleUnit somehow
+// nsStyleCoord is one way to do it, but there are other structs using pairs
+// of union and unit too
+
+impl nsStyleUnion {
+    /// Clean up any resources used by an nsStyleUnit
+    /// Currently, this only happens if the nsStyleUnit
+    /// is a Calc
+    pub unsafe fn reset(&mut self, unit: &mut nsStyleUnit) {
+        if *unit == nsStyleUnit::eStyleUnit_Calc {
+            Gecko_ResetStyleCoord(unit, self);
+        }
+    }
+
+    /// Set internal value to a calc() value
+    /// reset() the union before calling this
+    pub unsafe fn set_calc_value(&mut self, unit: &mut nsStyleUnit, v: nsStyleCoord_CalcValue) {
+        // Calc should have been cleaned up
+        assert!(*unit != nsStyleUnit::eStyleUnit_Calc);
+        Gecko_SetStyleCoordCalcValue(unit, self, v);
+    }
+
+    pub unsafe fn get_calc(&self) -> nsStyleCoord_CalcValue {
+        (*(*self.mPointer.as_ref() as *const nsStyleCoord_Calc))._base
+    }
+}