Oilpan: Prepare to move form control ua shadow elements to Oilpan heap.

Source/core/html/shadow/ClearButtonElement.h

Index: Source/core/html/shadow/ClearButtonElement.h
diff --git a/Source/core/html/shadow/ClearButtonElement.h b/Source/core/html/shadow/ClearButtonElement.h
index 6acf100bc6ca81adbf5cdb74e7a866b9e7a023f0..eba5309fa3097f7fb1422055de0ef9982bbf11a4 100644
--- a/Source/core/html/shadow/ClearButtonElement.h
+++ b/Source/core/html/shadow/ClearButtonElement.h
@@ -33,7 +33,7 @@ namespace WebCore {
 
 class ClearButtonElement FINAL : public HTMLDivElement {
 public:
-    class ClearButtonOwner {
+    class ClearButtonOwner : public WillBeGarbageCollectedMixin {
     public:
         virtual ~ClearButtonOwner() { }
         virtual void focusAndSelectClearButtonOwner() = 0;
@@ -41,9 +41,11 @@ public:
         virtual void clearValue() = 0;
     };
 
-    static PassRefPtr<ClearButtonElement> create(Document&, ClearButtonOwner&);
+    static PassRefPtrWillBeRawPtr<ClearButtonElement> create(Document&, ClearButtonOwner&);
     void releaseCapture();
-    void removeClearButtonOwner() { m_clearButtonOwner = 0; }
+    void removeClearButtonOwner() { m_clearButtonOwner = nullptr; }
+
+    virtual void trace(Visitor*) OVERRIDE;
 
 private:
     ClearButtonElement(Document&, ClearButtonOwner&);
@@ -52,7 +54,7 @@ private:
     virtual void defaultEventHandler(Event*) OVERRIDE;
     virtual bool isClearButtonElement() const OVERRIDE;
 
-    ClearButtonOwner* m_clearButtonOwner;
+    RawPtrWillBeMember<ClearButtonOwner> m_clearButtonOwner;
     bool m_capturing;
 };