Move the Widget hierarchy to the Oilpan heap.

Source/platform/Widget.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 15 matching lines @@
 
 #include "config.h"
 #include "platform/Widget.h"
 
 
 #include "wtf/Assertions.h"
 
 namespace blink {
 
 Widget::Widget()
-    : m_parent(0)
+    : m_parent(nullptr)
     , m_selfVisible(false)
     , m_parentVisible(false)
 {
 }
 
 Widget::~Widget()
 {
+#if !ENABLE(OILPAN)
     ASSERT(!parent());
+#endif
+}
+
+void Widget::trace(Visitor* visitor)
+{
+    visitor->trace(m_parent);
 }
 
 void Widget::setParent(Widget* widget)
 {
     ASSERT(!widget || !m_parent);
     if (!widget || !widget->isVisible())
         setParentVisible(false);
     m_parent = widget;
     if (widget && widget->isVisible())
         setParentVisible(true);
@@ skipping 105 matching lines @@
 {
     return point;
 }
 
 IntPoint Widget::convertSelfToChild(const Widget*, const IntPoint& point) const
 {
     return point;
 }
 
 } // namespace blink