Update animation when changes in animation keyframes are detected.

Source/core/css/CSSKeyframesRule.h

Index: Source/core/css/CSSKeyframesRule.h
diff --git a/Source/core/css/CSSKeyframesRule.h b/Source/core/css/CSSKeyframesRule.h
index ef9e45fb7086191b708951578d37ddcf48922d0e..c9c7ad6c55d7caa8ab9c90e8ed8c64d8cbe0483f 100644
--- a/Source/core/css/CSSKeyframesRule.h
+++ b/Source/core/css/CSSKeyframesRule.h
@@ -61,6 +61,9 @@ public:
 
     void traceAfterDispatch(Visitor*);
 
+    void styleChanged() { m_styleChangeCounter++; }
+    unsigned styleChangeCounter() const { return m_styleChangeCounter; }
+
 private:
     StyleRuleKeyframes();
     explicit StyleRuleKeyframes(const StyleRuleKeyframes&);
@@ -68,6 +71,7 @@ private:
     WillBeHeapVector<RefPtrWillBeMember<StyleKeyframe> > m_keyframes;
     AtomicString m_name;
     bool m_isPrefixed;
+    unsigned m_styleChangeCounter;
 };
 
 DEFINE_STYLE_RULE_TYPE_CASTS(Keyframes);