Auto merge of #17032 - jryans:stylo-visited, r=emilio

Stylo: visited pseudo-class support

Reviewed in https://bugzilla.mozilla.org/show_bug.cgi?id=1328509

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17032)
<!-- Reviewable:end -->

2 files changed, 16 insertions, 1 deletions

diff --git a/components/style/sharing/checks.rs b/components/style/sharing/checks.rs
index 5cc5869e509..4ac537e0009 100644
--- a/components/style/sharing/checks.rs
+++ b/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.
 ///
diff --git a/components/style/sharing/mod.rs b/components/style/sharing/mod.rs
index 744571ca863..67fde2e047b 100644
--- a/components/style/sharing/mod.rs
+++ b/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)
         }