Rollup merge of #17014 - hiikezoe:animation-rules-in-norma-restyle, r=emilio,birtles

Animation rules in norma restyle

<!-- Please describe your changes on the following line: -->

This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1366631 and https://bugzilla.mozilla.org/show_bug.cgi?id=1367225

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's for stylo

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components/style/rule_tree/mod.rs

@@ -8,7 +8,7 @@
 
 #[cfg(feature = "servo")]
 use heapsize::HeapSizeOf;
-use properties::{Importance, LonghandIdSet, PropertyDeclarationBlock};
+use properties::{AnimationRules, Importance, LonghandIdSet, PropertyDeclarationBlock};
 use shared_lock::{Locked, StylesheetGuards, SharedRwLockReadGuard};
 use smallvec::SmallVec;
 use std::io::{self, Write};
@@ -1142,6 +1142,56 @@ impl StrongRuleNode {
         }
         result
     }
+
+    /// Returns PropertyDeclarationBlock for this node.
+    /// This function must be called only for animation level node.
+    fn get_animation_style(&self) -> &Arc<Locked<PropertyDeclarationBlock>> {
+        debug_assert!(self.cascade_level().is_animation(),
+                      "The cascade level should be an animation level");
+        match *self.style_source().unwrap() {
+            StyleSource::Declarations(ref block) => block,
+            StyleSource::Style(_) => unreachable!("animating style should not be a style rule"),
+        }
+    }
+
+    /// Returns SMIL override declaration block if exists.
+    pub fn get_smil_animation_rule(&self) -> Option<&Arc<Locked<PropertyDeclarationBlock>>> {
+        if cfg!(feature = "servo") {
+            // Servo has no knowledge of a SMIL rule, so just avoid looking for it.
+            return None;
+        }
+
+        self.self_and_ancestors()
+            .take_while(|node| node.cascade_level() >= CascadeLevel::SMILOverride)
+            .find(|node| node.cascade_level() == CascadeLevel::SMILOverride)
+            .map(|node| node.get_animation_style())
+    }
+
+    /// Returns AnimationRules that has processed during animation-only restyles.
+    pub fn get_animation_rules(&self) -> AnimationRules {
+        if cfg!(feature = "servo") {
+            return AnimationRules(None, None);
+        }
+
+        let mut animation = None;
+        let mut transition = None;
+
+        for node in self.self_and_ancestors()
+                        .take_while(|node| node.cascade_level() >= CascadeLevel::Animations) {
+            match node.cascade_level() {
+                CascadeLevel::Animations => {
+                    debug_assert!(animation.is_none());
+                    animation = Some(node.get_animation_style())
+                },
+                CascadeLevel::Transitions => {
+                    debug_assert!(transition.is_none());
+                    transition = Some(node.get_animation_style())
+                },
+                _ => {},
+            }
+        }
+        AnimationRules(animation, transition)
+    }
 }
 
 /// An iterator over a rule node and its ancestors.