Style sharing cache for visited

The style sharing cache stores the regular `ComputedValues`, so it would also
have the visited values as well for anything inserted into the cache (since they
are nested inside).  Unlike all other element states, a change in state of
unvisited vs. visited does not change the style system's output, since we have
already computed both possible outputs up front.

We change the element state checks when looking for style sharing cache hits to
ignore visitedness, since that's handled by the two separate sets of values.

MozReview-Commit-ID: Dt8uK8gSQSP

components/style/sharing/checks.rs

@@ -8,6 +8,7 @@
 
 use context::{CurrentElementInfo, SelectorFlagsMap, SharedStyleContext};
 use dom::TElement;
+use element_state::*;
 use matching::MatchMethods;
 use selectors::bloom::BloomFilter;
 use selectors::matching::{ElementSelectorFlags, StyleRelations};
@@ -80,6 +81,20 @@ pub fn have_same_class<E>(element: E,
     element_class_attributes == *candidate.class_attributes.as_ref().unwrap()
 }
 
+/// Compare element and candidate state, but ignore visitedness.  Styles don't
+/// actually changed based on visitedness (since both possibilities are computed
+/// up front), so it's safe to share styles if visitedness differs.
+pub fn have_same_state_ignoring_visitedness<E>(element: E,
+                                               candidate: &StyleSharingCandidate<E>)
+                                               -> bool
+    where E: TElement,
+{
+    let state_mask = !IN_VISITED_OR_UNVISITED_STATE;
+    let state = element.get_state() & state_mask;
+    let candidate_state = candidate.element.get_state() & state_mask;
+    state == candidate_state
+}
+
 /// Whether a given element and a candidate match the same set of "revalidation"
 /// selectors.
 ///

components/style/sharing/mod.rs

@@ -349,7 +349,7 @@ impl<E: TElement> StyleSharingCandidateCache<E> {
             miss!(UserAndAuthorRules)
         }
 
-        if element.get_state() != candidate.element.get_state() {
+        if !checks::have_same_state_ignoring_visitedness(element, candidate) {
             miss!(State)
         }