blink/css: Read animation keyframe rules in UA sheets for shadow DOM.

third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp

Index: third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp b/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
index 2f576663e6ef833eda4cea6fa42d4172fb10743f..31527ca5f11e3f8d594ceabc2ba93eab29f13976 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
@@ -1214,6 +1214,20 @@ StyleRuleKeyframes* StyleResolver::FindKeyframesRule(
       return keyframes_rule;
   }
 
+  // This is a workaround for crbug.com/724975. Since the keyframe rules from
+  // UA style sheets are not available in the resolvers, read those rules
+  // directly here.
+  if (element->IsInShadowTree() &&
+      ToShadowRoot(element->GetTreeScope().RootNode()).GetType() ==
+          ShadowRootType::kUserAgent) {
+    const auto& keyframe_rules =
+        CSSDefaultStyleSheets::Instance().DefaultStyle()->KeyframesRules();
+    for (const auto& rule : keyframe_rules) {
+      if (rule->GetName() == animation_name)
+        return rule;
+    }
+  }
+
   for (auto& resolver : resolvers)
     resolver->SetHasUnresolvedKeyframesRule();
   return nullptr;