From 9c054819233e53cc21fab68bbf7b6a8128d886ac Mon Sep 17 00:00:00 2001
From: Hiroyuki Ikezoe <hikezoe@mozilla.com>
Date: Tue, 18 Jul 2017 19:14:22 +0900
Subject: [PATCH] Skip snapshot handling during animation-only restyle.

---
 components/style/data.rs      |  5 +++++
 components/style/traversal.rs | 11 ++++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/components/style/data.rs b/components/style/data.rs
index 5d2771121a1..9ddd20c0dce 100644
--- a/components/style/data.rs
+++ b/components/style/data.rs
@@ -241,6 +241,11 @@ impl ElementData {
         element: E,
         shared_context: &SharedStyleContext)
     {
+        // In animation-only restyle we shouldn't touch snapshot at all.
+        if shared_context.traversal_flags.for_animation_only() {
+            return;
+        }
+
         use invalidation::element::invalidator::TreeStyleInvalidator;
 
         debug!("invalidate_style_if_needed: {:?}, flags: {:?}, has_snapshot: {}, \
diff --git a/components/style/traversal.rs b/components/style/traversal.rs
index 663ae72a433..689967da295 100644
--- a/components/style/traversal.rs
+++ b/components/style/traversal.rs
@@ -235,7 +235,9 @@ pub trait DomTraversal<E: TElement> : Sync {
             // Look at whether there has been any attribute or state change, and
             // invalidate our style, and the one of our siblings and descendants as
             // needed.
-            data.invalidate_style_if_needed(root, shared_context);
+            if !flags.for_animation_only() {
+                data.invalidate_style_if_needed(root, shared_context);
+            }
 
             let parent = root.traversal_parent();
             let parent_data = match parent {
@@ -523,7 +525,8 @@ where
 {
     context.thread_local.begin_element(element, data);
     context.thread_local.statistics.elements_traversed += 1;
-    debug_assert!(!element.has_snapshot() || element.handled_snapshot(),
+    debug_assert!(context.shared.traversal_flags.for_animation_only() ||
+                  !element.has_snapshot() || element.handled_snapshot(),
                   "Should've handled snapshots here already");
 
     let compute_self =
@@ -810,7 +813,9 @@ where
         // as needed.
         //
         // NB: This will be a no-op if there's no snapshot.
-        child_data.invalidate_style_if_needed(child, &context.shared);
+        if !flags.for_animation_only() {
+            child_data.invalidate_style_if_needed(child, &context.shared);
+        }
 
         if D::element_needs_traversal(child, flags, &*child_data, Some(data)) {
             note_child(child_node);