Oilpan: Fix SVGElement leaks introduced in 201698

The Persistent handle introduced to SVGInterpolation in 201698 created the following cycle.

SVGInterporation =(Persistent)=>
SVGAnimatedProperty =(Member)=>
SVGElement =(Member)=>
ElementRareData =(Member)=>
ElementAnimations =(part of object)=>
CSSAnimations =(part of object)=>
CSSAnimationUpdate =(Member)=>
NewTransition =(Member)=>
InertEffect =(Member)=>
EffectModel =(RefPtr)=>
InterpolationEffect =(RefPtr)=>
InterpolationRecord =(RefPtr)=>
SVGInterpolation

This CL breaks the cycle by making SVGAnimatedProperty::m_contextElement a raw pointer.

BUG=

Review URL: https://codereview.chromium.org/1325433005

git-svn-id: svn://svn.chromium.org/blink/trunk@201779 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/svg/properties/SVGAnimatedProperty.h

@@ -92,7 +92,6 @@ public:
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
-        visitor->trace(m_contextElement);
     }
 
 protected:
@@ -103,7 +102,22 @@ private:
     bool m_isReadOnly;
 
     // This reference is kept alive from V8 wrapper
-    RawPtrWillBeMember<SVGElement> m_contextElement;
+    // TODO(oilpan): This should be a Member. Currently we cannot do it because
+    // it creates a cycle as follows:
+    // SVGInterporation =(Persistent)=>
+    // SVGAnimatedProperty =(Member)=>
+    // SVGElement =(Member)=>
+    // ElementRareData =(Member)=>
+    // ElementAnimations =(part of object)=>
+    // CSSAnimations =(part of object)=>
+    // CSSAnimationUpdate =(Member)=>
+    // NewTransition =(Member)=>
+    // InertEffect =(Member)=>
+    // EffectModel =(RefPtr)=>
+    // InterpolationEffect =(RefPtr)=>
+    // InterpolationRecord =(RefPtr)=>
+    // SVGInterpolation
+    SVGElement* m_contextElement;
 
     const QualifiedName& m_attributeName;
 };