style: Remove the display: -moz-box overrides display: -webkit-box hack.

display: -moz-box is no longer exposed to content so this is not necessary.

See bug 1407701 for context.

Differential Revision: https://phabricator.services.mozilla.com/D12961

components/style/properties/declaration_block.rs

@@ -462,22 +462,6 @@ impl PropertyDeclarationBlock {
                     return false;
                 }
 
-                // As a compatibility hack, specially on Android,
-                // don't allow to override a prefixed webkit display
-                // value with an unprefixed version from parsing
-                // code.
-                //
-                // TODO(emilio): Unship.
-                if let PropertyDeclaration::Display(old_display) = *slot {
-                    use crate::properties::longhands::display::computed_value::T as display;
-
-                    if let PropertyDeclaration::Display(new_display) = declaration {
-                        if display::should_ignore_parsed_value(old_display, new_display) {
-                            return false;
-                        }
-                    }
-                }
-
                 index_to_remove = Some(i);
                 break;
             }

components/style/values/specified/box.rs

@@ -178,30 +178,6 @@ impl Display {
         }
     }
 
-    /// Whether `new_display` should be ignored, given a previous
-    /// `old_display` value.
-    ///
-    /// This is used to ignore `display: -moz-box` declarations after an
-    /// equivalent `display: -webkit-box` declaration, since the former
-    /// has a vastly different meaning. See bug 1107378 and bug 1407701.
-    ///
-    /// FIXME(emilio): This is a pretty decent hack, we should try to
-    /// remove it.
-    pub fn should_ignore_parsed_value(_old_display: Self, _new_display: Self) -> bool {
-        #[cfg(feature = "gecko")]
-        {
-            match (_old_display, _new_display) {
-                (Display::WebkitBox, Display::MozBox) |
-                (Display::WebkitInlineBox, Display::MozInlineBox) => {
-                    return true;
-                },
-                _ => {},
-            }
-        }
-
-        return false;
-    }
-
     /// Returns whether this "display" value is one of the types for
     /// ruby.
     #[cfg(feature = "gecko")]