style: Use Rust types for some misc properties.

-moz-tab-size, border-image-outset and border-image-slice.

This is not a particularly interesting patch, just removes some code. We can
remove way more code when a few related properties are also ported.

Differential Revision: https://phabricator.services.mozilla.com/D19825

components/style/properties/longhands/border.mako.rs

@@ -119,10 +119,9 @@ ${helpers.predefined_type(
 
 ${helpers.predefined_type(
     "border-image-outset",
-    "LengthOrNumberRect",
-    parse_method="parse_non_negative",
-    initial_value="computed::LengthOrNumberRect::all(computed::LengthOrNumber::zero())",
-    initial_specified_value="specified::LengthOrNumberRect::all(specified::LengthOrNumber::zero())",
+    "NonNegativeLengthOrNumberRect",
+    initial_value="generics::rect::Rect::all(computed::NonNegativeLengthOrNumber::zero())",
+    initial_specified_value="generics::rect::Rect::all(specified::NonNegativeLengthOrNumber::zero())",
     spec="https://drafts.csswg.org/css-backgrounds/#border-image-outset",
     animation_value_type="discrete",
     flags="APPLIES_TO_FIRST_LETTER",