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

Source/core/html/shadow/SpinButtonElement.h

Index: Source/core/html/shadow/SpinButtonElement.h
diff --git a/Source/core/html/shadow/SpinButtonElement.h b/Source/core/html/shadow/SpinButtonElement.h
index 231b2200093fbcbf184c73171be99210fce7d5c3..d29fdbe4b47010e07ddf76e644715a0f83a7c24b 100644
--- a/Source/core/html/shadow/SpinButtonElement.h
+++ b/Source/core/html/shadow/SpinButtonElement.h
@@ -44,7 +44,7 @@ public:
         EventDispatchAllowed,
         EventDispatchDisallowed,
     };
-    class SpinButtonOwner {
+    class SpinButtonOwner : public WillBeGarbageCollectedMixin {
     public:
         virtual ~SpinButtonOwner() { }
         virtual void focusAndSelectSpinButtonOwner() = 0;
@@ -61,7 +61,7 @@ public:
     static PassRefPtr<SpinButtonElement> create(Document&, SpinButtonOwner&);
     UpDownState upDownState() const { return m_upDownState; }
     void releaseCapture(EventDispatch = EventDispatchAllowed);
-    void removeSpinButtonOwner() { m_spinButtonOwner = 0; }
+    void removeSpinButtonOwner() { m_spinButtonOwner = nullptr; }
 
     void step(int amount);
 
@@ -70,6 +70,8 @@ public:
 
     void forwardEvent(Event*);
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     SpinButtonElement(Document&, SpinButtonOwner&);
 
@@ -88,7 +90,7 @@ private:
     bool shouldRespondToMouseEvents();
     virtual bool isMouseFocusable() const OVERRIDE { return false; }
 
-    SpinButtonOwner* m_spinButtonOwner;
+    RawPtrWillBeMember<SpinButtonOwner> m_spinButtonOwner;
     bool m_capturing;
     UpDownState m_upDownState;
     UpDownState m_pressStartingState;