Change CSSParserContext to have a Document handle (vs UseCounter).

third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp

Index: third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp b/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
index 88cae61ce48c759a844bafe5a82910b0f8a098a8..f80fd37122b70ae8a87f947f367f92cfbab00d6a 100644
--- a/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
+++ b/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
@@ -173,8 +173,12 @@ CSSKeyframeRule* CSSKeyframesRule::item(unsigned index) const {
 
 CSSKeyframeRule* CSSKeyframesRule::anonymousIndexedGetter(
     unsigned index) const {
-  if (UseCounter* useCounter = UseCounter::getFrom(parentStyleSheet()))
-    useCounter->count(UseCounter::CSSKeyframesRuleAnonymousIndexedGetter);
+  const Document* parentDocument =
+      CSSStyleSheet::singleOwnerDocument(parentStyleSheet());
+  if (parentDocument) {
+    UseCounter::count(*parentDocument,
+                      UseCounter::CSSKeyframesRuleAnonymousIndexedGetter);
+  }
   return item(index);
 }