Store selectors and combinators inline in a single sequence.

This improves cache locality and reduces allocations during parsing.

Note that this reverses the iteration order within a sequence of simple selectors,
but that shouldn't matter.

components/selectors/visitor.rs

@@ -6,7 +6,8 @@
 
 #![deny(missing_docs)]
 
-use parser::{AttrSelector, Combinator, ComplexSelector, SelectorImpl, SimpleSelector};
+use parser::{AttrSelector, Combinator, SelectorImpl};
+use parser::{SelectorIter, SimpleSelector};
 
 /// A trait to visit selector properties.
 ///
@@ -33,7 +34,7 @@ pub trait SelectorVisitor {
     /// Gets the combinator to the right of the selector, or `None` if the
     /// selector is the leftmost one.
     fn visit_complex_selector(&mut self,
-                              _: &ComplexSelector<Self::Impl>,
+                              _: SelectorIter<Self::Impl>,
                               _combinator_to_right: Option<Combinator>)
                               -> bool {
         true