Move the Widget hierarchy to the Oilpan heap.

Source/platform/scroll/Scrollbar.cpp

 /*
  * Copyright (C) 2004, 2006, 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 #include "platform/scroll/ScrollbarTheme.h"
 
 #if ((OS(POSIX) && !OS(MACOSX)) || OS(WIN))
 // The position of the scrollbar thumb affects the appearance of the steppers, so
 // when the thumb moves, we have to invalidate them for painting.
 #define THUMB_POSITION_AFFECTS_BUTTONS
 #endif
 
 namespace blink {
 
-PassRefPtr<Scrollbar> Scrollbar::create(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize size)
+PassRefPtrWillBeRawPtr<Scrollbar> Scrollbar::create(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize size)
 {
-    return adoptRef(new Scrollbar(scrollableArea, orientation, size));
+    return adoptRefWillBeNoop(new Scrollbar(scrollableArea, orientation, size));
 }
 
 Scrollbar::Scrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize controlSize, ScrollbarTheme* theme)
     : m_scrollableArea(scrollableArea)
     , m_orientation(orientation)
     , m_controlSize(controlSize)
     , m_theme(theme)
     , m_visibleSize(0)
     , m_totalSize(0)
     , m_currentPos(0)
@@ skipping 15 matching lines @@
 
     m_theme->registerScrollbar(this);
 
     // FIXME: This is ugly and would not be necessary if we fix cross-platform code to actually query for
     // scrollbar thickness and use it when sizing scrollbars (rather than leaving one dimension of the scrollbar
     // alone when sizing).
     int thickness = m_theme->scrollbarThickness(controlSize);
     Widget::setFrameRect(IntRect(0, 0, thickness, thickness));
 
     m_currentPos = scrollableAreaCurrentPos();
+
+#if ENABLE(OILPAN)
+    if (m_scrollableArea)
+        m_animator = m_scrollableArea->scrollAnimator();

[haraken, 2014/10/10 02:50:32]

Sorry, I got confused with this again.

The scrollableArea is off-heap. So it should be OK to touch
m_scrollableArea->m_animator in ~Scrollbar(). Then we won't need m_animator,
will we?

[sof, 2014/10/10 05:22:19]

It _might_ be on the heap, we don't know (i.e., a FrameView is.)

+#endif
 }
 
 Scrollbar::~Scrollbar()
 {
     stopTimerIfNeeded();
 
     m_theme->unregisterScrollbar(this);
+
+#if ENABLE(OILPAN)
+    if (!m_animator)
+        return;
+
+    ASSERT(m_scrollableArea);
+    if (m_orientation == VerticalScrollbar)
+        m_animator->willRemoveVerticalScrollbar(this);
+    else
+        m_animator->willRemoveHorizontalScrollbar(this);
+#endif
 }
 
 ScrollbarOverlayStyle Scrollbar::scrollbarOverlayStyle() const
 {
     return m_scrollableArea ? m_scrollableArea->scrollbarOverlayStyle() : ScrollbarOverlayStyleDefault;
 }
 
 void Scrollbar::getTickmarks(Vector<IntRect>& tickmarks) const
 {
     if (m_scrollableArea)
@@ skipping 25 matching lines @@
     if (position == m_currentPos)
         return;
 
     int oldThumbPosition = theme()->thumbPosition(this);
     m_currentPos = position;
     updateThumbPosition();
     if (m_pressedPart == ThumbPart)
         setPressedPos(m_pressedPos + theme()->thumbPosition(this) - oldThumbPosition);
 }
 
+void Scrollbar::disconnectFromScrollableArea()
+{
+    m_scrollableArea = nullptr;
+#if ENABLE(OILPAN)
+    m_animator = nullptr;
+#endif
+}
+
 void Scrollbar::setProportion(int visibleSize, int totalSize)
 {
     if (visibleSize == m_visibleSize && totalSize == m_totalSize)
         return;
 
     m_visibleSize = visibleSize;
     m_totalSize = totalSize;
 
     updateThumbProportion();
 }
@@ skipping 387 matching lines @@
     if (!m_scrollableArea)
         return 0;
 
     if (m_orientation == HorizontalScrollbar)
         return m_scrollableArea->scrollPosition().x() - m_scrollableArea->minimumScrollPosition().x();
 
     return m_scrollableArea->scrollPosition().y() - m_scrollableArea->minimumScrollPosition().y();
 }
 
 } // namespace blink