[oilpan] The Node hierarchy should have correct accept method chains

Source/core/html/ImageDocument.cpp

Index: Source/core/html/ImageDocument.cpp
diff --git a/Source/core/html/ImageDocument.cpp b/Source/core/html/ImageDocument.cpp
index 39b5a0e1d946514921ce39f3abb2d291e679e9bf..3f9ffe74f1866c7f0c01517bd11bcfac07444e86 100644
--- a/Source/core/html/ImageDocument.cpp
+++ b/Source/core/html/ImageDocument.cpp
@@ -101,6 +101,8 @@ class ImageDocumentElement : public HTMLImageElement {
 public:
     static PassRefPtr<ImageDocumentElement> create(ImageDocument*);
 
+    void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     // FIXME(oilpan): handlify ImageDocument.
     ImageDocumentElement(ImageDocument* document)
@@ -386,6 +388,12 @@ bool ImageEventListener::operator==(const EventListener& listener)
     return false;
 }
 
+void ImageDocument::acceptHeapVisitor(Visitor* visitor) const
+{
+    visitor->visit(m_imageElement);
+    HTMLDocument::acceptHeapVisitor(visitor);
+}
+
 // --------
 
 ImageDocumentElement::~ImageDocumentElement()
@@ -403,4 +411,9 @@ void ImageDocumentElement::didMoveToNewDocument(Handle<Document> oldDocument)
     HTMLImageElement::didMoveToNewDocument(oldDocument);
 }
 
+void ImageDocumentElement::acceptHeapVisitor(Visitor* visitor) const
+{
+    HTMLImageElement::acceptHeapVisitor(visitor);
+}
+
 }