Adding @keyframes rules only affects TreeScope plus host.

third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h

Index: third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
diff --git a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
index 58f4e0b9552a81ef195575949052a15936d3dcbc..8d4ba30a854c1906d86964b101fe21760f5ccb9c 100644
--- a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
+++ b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
@@ -62,6 +62,8 @@ public:
     void resetAuthorStyle();
     void collectViewportRulesTo(ViewportStyleResolver*) const;
     bool hasDeepOrShadowSelector() const { return m_hasDeepOrShadowSelector; }
+    void setHasUnresolvedKeyframesRule() { m_hasUnresolvedKeyframesRule = true; }
+    static void keyframesRulesAdded(const TreeScope&);
 
     DECLARE_TRACE();
 
@@ -108,6 +110,7 @@ private:
 
     Member<CSSStyleSheetRuleSubSet> m_treeBoundaryCrossingRuleSet;
     bool m_hasDeepOrShadowSelector = false;
+    bool m_hasUnresolvedKeyframesRule = false;
 };
 
 } // namespace blink