style: Fix the default behavior of scale:<number>{1}.

The current spec says: "If only the X value is given, the Y value
defaults to the same value.", so we should update the behavior.

Besides, we also update the serialization, so we serialization both
specified and computed value by servo. We enable the preference
for all the css-transforms, so some of them are passed now.

Differential Revision: https://phabricator.services.mozilla.com/D10638

components/style/values/generics/transform.rs

@@ -7,6 +7,8 @@
 use app_units::Au;
 use euclid::{self, Rect, Transform3D};
 use num_traits::Zero;
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ToCss};
 use values::computed::length::Length as ComputedLength;
 use values::computed::length::LengthOrPercentage as ComputedLengthOrPercentage;
 use values::specified::angle::Angle as SpecifiedAngle;
@@ -560,7 +562,6 @@ pub enum Rotate<Number, Angle> {
     SpecifiedValueInfo,
     ToAnimatedZero,
     ToComputedValue,
-    ToCss,
 )]
 /// A value of the `Scale` property
 ///
@@ -568,14 +569,38 @@ pub enum Rotate<Number, Angle> {
 pub enum Scale<Number> {
     /// 'none'
     None,
-    /// '<number>'
-    ScaleX(Number),
-    /// '<number>{2}'
+    /// '<number>{1,2}'
     Scale(Number, Number),
     /// '<number>{3}'
     Scale3D(Number, Number, Number),
 }
 
+impl<Number: ToCss + PartialEq> ToCss for Scale<Number> {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        match self {
+            &Scale::None => dest.write_str("none"),
+            &Scale::Scale(ref x, ref y) => {
+                x.to_css(dest)?;
+                if x != y {
+                    dest.write_char(' ')?;
+                    y.to_css(dest)?;
+                }
+                Ok(())
+            },
+            &Scale::Scale3D(ref x, ref y, ref z) => {
+                x.to_css(dest)?;
+                dest.write_char(' ')?;
+                y.to_css(dest)?;
+                dest.write_char(' ')?;
+                z.to_css(dest)
+            },
+        }
+    }
+}
+
 #[derive(
     Clone,
     ComputeSquaredDistance,