Make source_order u32 and shrink Rule.

MozReview-Commit-ID: AKNTZZqke1O

components/style/stylist.rs

@@ -121,7 +121,7 @@ pub struct Stylist {
 
     /// A monotonically increasing counter to represent the order on which a
     /// style rule appears in a stylesheet, needed to sort them by source order.
-    rules_source_order: usize,
+    rules_source_order: u32,
 
     /// Selector dependencies used to compute restyle hints.
     dependencies: DependencySet,
@@ -1497,11 +1497,11 @@ pub struct Rule {
     /// The ancestor hashes associated with the selector.
     #[cfg_attr(feature = "servo", ignore_heap_size_of = "No heap data")]
     pub hashes: AncestorHashes,
+    /// The source order this style rule appears in.
+    pub source_order: u32,
     /// The actual style rule.
     #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
     pub style_rule: Arc<Locked<StyleRule>>,
-    /// The source order this style rule appears in.
-    pub source_order: usize,
 }
 
 impl SelectorMapEntry for Rule {
@@ -1537,7 +1537,7 @@ impl Rule {
     pub fn new(selector: Selector<SelectorImpl>,
                hashes: AncestorHashes,
                style_rule: Arc<Locked<StyleRule>>,
-               source_order: usize)
+               source_order: u32)
                -> Self
     {
         Rule {
@@ -1561,7 +1561,7 @@ pub struct ApplicableDeclarationBlock {
     #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
     pub source: StyleSource,
     /// The source order of this block.
-    pub source_order: usize,
+    pub source_order: u32,
     /// The specificity of the selector this block is represented by.
     pub specificity: u32,
     /// The cascade level this applicable declaration block is in.

tests/unit/style/stylist.rs

@@ -45,7 +45,7 @@ fn get_mock_rules(css_selectors: &[&str]) -> (Vec<Vec<Rule>>, SharedRwLock) {
         let guard = shared_lock.read();
         let rule = locked.read_with(&guard);
         rule.selectors.0.iter().map(|s| {
-            Rule::new(s.selector.clone(), s.hashes.clone(), locked.clone(), i)
+            Rule::new(s.selector.clone(), s.hashes.clone(), locked.clone(), i as u32)
         }).collect()
     }).collect(), shared_lock)
 }

tests/unit/stylo/size_of.rs

@@ -27,7 +27,7 @@ fn size_of_selectors_dummy_types() {
 // The size of this is critical to performance on the bloom-basic microbenchmark.
 // When iterating over a large Rule array, we want to be able to fast-reject
 // selectors (with the inline hashes) with as few cache misses as possible.
-size_of_test!(test_size_of_rule, style::stylist::Rule, 40);
+size_of_test!(test_size_of_rule, style::stylist::Rule, 32);
 
 size_of_test!(test_size_of_option_arc_cv, Option<Arc<ComputedValues>>, 8);
 size_of_test!(test_size_of_option_rule_node, Option<StrongRuleNode>, 8);