style: Use Rust sizes for flex-basis, width, height, and their min/max properties.

Really sorry for the size of the patch :(

Only intentional behavior change is in the uses of HasLengthAndPercentage(),
where it's easier to do the right thing. The checks that used to check for
(IsCalcUnit() && CalcHasPercentage()) are wrong since bug 957915.

Differential Revision: https://phabricator.services.mozilla.com/D19553

components/style/values/computed/flex.rs

@@ -14,6 +14,6 @@ impl FlexBasis {
     /// `auto`
     #[inline]
     pub fn auto() -> Self {
-        GenericFlexBasis::Width(Size::auto())
+        GenericFlexBasis::Size(Size::auto())
     }
 }