Store pristine element state rather than a set of changes.

This is the strategy we'll need to take for attributes, and so this change
puts us in a position to handle attributes and state the same way.

This does mean that we stop taking care to track the situations where our
state has reverted to the original state, with no net change. I think that's
probably of negligible value though.

2 files changed, 6 insertions, 7 deletions

diff --git a/components/layout/layout_task.rs b/components/layout/layout_task.rs
index 7a615b02f6b..bdf1b613562 100644
--- a/components/layout/layout_task.rs
+++ b/components/layout/layout_task.rs
@@ -1213,13 +1213,12 @@ impl LayoutTask {
             }
         }
 
-        let state_changes = document.drain_element_state_changes();
+        let modified_elements = document.drain_modified_elements();
         if !needs_dirtying {
-            for &(el, state_change) in state_changes.iter() {
-                debug_assert!(!state_change.is_empty());
+            for &(el, old_state) in modified_elements.iter() {
                 let hint = rw_data.stylist.restyle_hint_for_state_change(&el,
                                                                          el.get_state(),
-                                                                         state_change);
+                                                                         old_state);
                 el.note_restyle_hint(hint);
             }
         }
diff --git a/components/layout/wrapper.rs b/components/layout/wrapper.rs
index 04d3470fb64..ae8462426e8 100644
--- a/components/layout/wrapper.rs
+++ b/components/layout/wrapper.rs
@@ -375,10 +375,10 @@ impl<'le> LayoutDocument<'le> {
         self.as_node().children().find(LayoutNode::is_element)
     }
 
-    pub fn drain_element_state_changes(&self) -> Vec<(LayoutElement, ElementState)> {
+    pub fn drain_modified_elements(&self) -> Vec<(LayoutElement, ElementState)> {
         unsafe {
-            let changes = self.document.drain_element_state_changes();
-            Vec::from_iter(changes.iter().map(|&(el, state)|
+            let elements = self.document.drain_modified_elements();
+            Vec::from_iter(elements.iter().map(|&(el, state)|
                 (LayoutElement {
                     element: el,
                     chain: PhantomData,