Oilpan: KeyframeEffect::m_target shouldn't become stale

Source/core/animation/ElementAnimations.h

Index: Source/core/animation/ElementAnimations.h
diff --git a/Source/core/animation/ElementAnimations.h b/Source/core/animation/ElementAnimations.h
index fc6b4827600b99effca611d166d2a9e7b0388d3f..0b4ed0d64d74091067151559509dcdcb59c69a24 100644
--- a/Source/core/animation/ElementAnimations.h
+++ b/Source/core/animation/ElementAnimations.h
@@ -74,6 +74,10 @@ public:
     void updateBaseComputedStyle(const ComputedStyle*);
     void clearBaseComputedStyle();
 
+#if !ENABLE(OILPAN)
+    void addEffect(KeyframeEffect* effect) { m_effects.add(effect); }
+#endif
+
     DECLARE_TRACE();
 
 private:
@@ -85,6 +89,12 @@ private:
     bool m_animationStyleChange;
     RefPtr<ComputedStyle> m_baseComputedStyle;
 
+#if !ENABLE(OILPAN)
+    // TODO(oilpan): This is to avoid a reference cycle that keeps Elements
+    // alive and won't be needed once the Node hierarchy becomes traceable.
+    HeapHashSet<WeakMember<KeyframeEffect>> m_effects;
+#endif
+
     // CSSAnimations and DeferredLegacyStyleInterpolation checks if a style change is due to animation.
     friend class CSSAnimations;
     friend class DeferredLegacyStyleInterpolation;