style: Move MozLength and MaxLength into generics.

Move MozLength and MaxLength into generics, and drop the manual implementation
of ToComputedValue.

Differential Revision: https://phabricator.services.mozilla.com/D8291

components/style/values/generics/length.rs

@@ -0,0 +1,54 @@
+/* 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/. */
+
+//! Generic types for CSS values related to length.
+
+use values::computed::ExtremumLength;
+
+/// A generic value for the `width`, `height`, `min-width`, or `min-height` property.
+///
+/// Unlike `max-width` or `max-height` properties, a MozLength can be `auto`,
+/// and cannot be `none`.
+///
+/// Note that it only accepts non-negative values.
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+)]
+pub enum MozLength<LengthOrPercentageOrAuto> {
+    LengthOrPercentageOrAuto(LengthOrPercentageOrAuto),
+    #[animation(error)]
+    ExtremumLength(ExtremumLength),
+}
+
+/// A generic value for the `max-width` or `max-height` property.
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss
+)]
+pub enum MaxLength<LengthOrPercentageOrNone> {
+    LengthOrPercentageOrNone(LengthOrPercentageOrNone),
+    #[animation(error)]
+    ExtremumLength(ExtremumLength),
+}