Auto merge of #14464 - canaltinova:cssom-test, r=Manishearth

Write tests for CSSOM Interfaces

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ToCss implementation was wrong about Keyframe percentage values, it was writing values between 0-1. I had to fix it. Wrote some tests about CSSKeyframesRule, CSSNamespaceRule, CSSRuleList, CSSStyleSheet, StyleSheetList interfaces.
CSSFontFaceRule and CSSViewportRule looks like not implemented yet. I didn't write one for them.
Also name attribute in CSSKeyframesRule isn't implemented yet. Is there any complication about it? If not, I can implement it.

r? @Manishearth

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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- [X] There are tests for these changes OR

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components/style/keyframes.rs

@@ -14,7 +14,7 @@ use std::sync::Arc;
 use style_traits::ToCss;
 use stylesheets::{MemoryHoleReporter, Stylesheet};
 
-/// A number from 1 to 100, indicating the percentage of the animation where
+/// A number from 0 to 1, indicating the percentage of the animation where
 /// this keyframe should run.
 #[derive(Debug, Copy, Clone, PartialEq, PartialOrd)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
@@ -30,6 +30,12 @@ impl ::std::cmp::Ord for KeyframePercentage {
 
 impl ::std::cmp::Eq for KeyframePercentage { }
 
+impl ToCss for KeyframePercentage {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        write!(dest, "{}%", self.0 * 100.0)
+    }
+}
+
 impl KeyframePercentage {
     #[inline]
     pub fn new(value: f32) -> KeyframePercentage {
@@ -93,10 +99,10 @@ pub struct Keyframe {
 impl ToCss for Keyframe {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
         let mut iter = self.selector.percentages().iter();
-        try!(write!(dest, "{}%", iter.next().unwrap().0));
+        try!(iter.next().unwrap().to_css(dest));
         for percentage in iter {
             try!(write!(dest, ", "));
-            try!(write!(dest, "{}%", percentage.0));
+            try!(percentage.to_css(dest));
         }
         try!(dest.write_str(" { "));
         try!(self.block.read().to_css(dest));