Change StyleResolver::document() to be private

Source/core/animation/css/CSSAnimations.cpp

Index: Source/core/animation/css/CSSAnimations.cpp
diff --git a/Source/core/animation/css/CSSAnimations.cpp b/Source/core/animation/css/CSSAnimations.cpp
index 7bed2fd97fda28fe6b254dc20bc0c3f2194301a1..88aad824671c0dc3fab900f093cb219bbe064a77 100644
--- a/Source/core/animation/css/CSSAnimations.cpp
+++ b/Source/core/animation/css/CSSAnimations.cpp
@@ -202,7 +202,7 @@ static void resolveKeyframes(StyleResolver* resolver, const Element* animatingEl
 const StyleRuleKeyframes* CSSAnimations::matchScopedKeyframesRule(StyleResolver* resolver, const Element* element, const StringImpl* animationName)
 {
     // FIXME: This is all implementation detail of style resolver, CSSAnimations shouldn't be reaching into any of it.
-    if (resolver->document().styleEngine()->hasOnlyScopedResolverForDocument())
+    if (element->document().styleEngine()->hasOnlyScopedResolverForDocument())
         return element->document().scopedStyleResolver()->keyframeStylesForAnimation(animationName);
 
     WillBeHeapVector<RawPtrWillBeMember<ScopedStyleResolver>, 8> stack;