style: Remove PseudoElement::inherits_all.

I plan to change servo to use all: inherit on its UA sheet.

I hope the patch below should make it good enough performance-wise. And also,
it's probably broken so I don't think it's worth supporting it specially.

Differential Revision: https://phabricator.services.mozilla.com/D8686

components/style/gecko/pseudo_element.rs

@@ -57,15 +57,6 @@ impl PseudoElement {
         PseudoElementCascadeType::Lazy
     }
 
-    /// Whether cascading this pseudo-element makes it inherit all properties,
-    /// even reset ones.
-    ///
-    /// This is used in Servo for anonymous boxes, though it's likely broken.
-    #[inline]
-    pub fn inherits_all(&self) -> bool {
-        false
-    }
-
     /// Whether the pseudo-element should inherit from the default computed
     /// values instead of from the parent element.
     ///

components/style/properties/properties.mako.rs

@@ -3298,15 +3298,6 @@ impl<'a> StyleBuilder<'a> {
         let reset_style = device.default_computed_values();
         let inherited_style = parent_style.unwrap_or(reset_style);
         let inherited_style_ignoring_first_line = parent_style_ignoring_first_line.unwrap_or(reset_style);
-        // FIXME(bz): inherits_all seems like a fundamentally broken idea.  I'm
-        // 99% sure it should give incorrect behavior for table anonymous box
-        // backgrounds, for example.  This code doesn't attempt to make it play
-        // nice with inherited_style_ignoring_first_line.
-        let reset_style = if pseudo.map_or(false, |p| p.inherits_all()) {
-            inherited_style
-        } else {
-            reset_style
-        };
 
         let flags = inherited_style.flags.inherited();
 

components/style/servo/selector_parser.rs

@@ -221,11 +221,6 @@ impl PseudoElement {
         }
     }
 
-    /// To be removed.
-    pub fn inherits_all(&self) -> bool {
-        false
-    }
-
     /// Covert non-canonical pseudo-element to canonical one, and keep a
     /// canonical one as it is.
     pub fn canonical(&self) -> PseudoElement {

components/style/stylist.rs

@@ -614,14 +614,6 @@ impl Stylist {
 
     /// Computes the style for a given "precomputed" pseudo-element, taking the
     /// universal rules and applying them.
-    ///
-    /// If `inherit_all` is true, then all properties are inherited from the
-    /// parent; otherwise, non-inherited properties are reset to their initial
-    /// values. The flow constructor uses this flag when constructing anonymous
-    /// flows.
-    ///
-    /// TODO(emilio): The type parameter could go away with a void type
-    /// implementing TElement.
     pub fn precomputed_values_for_pseudo<E>(
         &self,
         guards: &StylesheetGuards,