Add infrastructure for partial layouts

Source/core/rendering/RenderObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 49 matching lines @@
 class RenderInline;
 class RenderBlock;
 class RenderFlowThread;
 class RenderGeometryMap;
 class RenderLayer;
 class RenderLayerModelObject;
 class RenderNamedFlowThread;
 class RenderSVGResourceContainer;
 class RenderTable;
 class RenderTheme;
+class RenderView;
 class TransformState;
 
 struct PaintInfo;
 
 enum CursorDirective {
     SetCursorBasedOnStyle,
     SetCursor,
     DoNotSetCursor
 };
 
@@ skipping 587 matching lines @@
 
     // Recursive function that computes the size and position of this object and all its descendants.
     virtual void layout();
 
     /* This function performs a layout only if one is needed. */
     void layoutIfNeeded() { if (needsLayout()) layout(); }
 
     void forceLayout();
     void forceChildLayout();
 
+    // True if we can abort layout, leaving a partially laid out tree.
+    virtual bool supportsPartialLayout() const { return false; }
+
     // used for element state updates that cannot be fixed with a
     // repaint and do not need a relayout
     virtual void updateFromElement() { }
 
     virtual void addAnnotatedRegions(Vector<AnnotatedRegionValue>&);
     void collectAnnotatedRegions(Vector<AnnotatedRegionValue>&);
 
     bool isComposited() const;
 
     bool hitTest(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestFilter = HitTestAll);
@@ skipping 379 matching lines @@
         StyleColor styleColor = color;
         for (const RenderObject* object = this; UNLIKELY(styleColor.isCurrentColor()) && object && object->style(); object = object->parent())
             styleColor = object->style()->visitedDependentColor(CSSPropertyColor);
         return styleColor;
     }
 
     void removeShapeImageClient(ShapeValue*);
 
 #ifndef NDEBUG
     void checkBlockPositionedObjectsNeedLayout();
+    void checkNotInPartialLayout();
 #endif
 
     RefPtr<RenderStyle> m_style;
 
     Node* m_node;
 
     RenderObject* m_parent;
     RenderObject* m_previous;
     RenderObject* m_next;
 
@@ skipping 150 matching lines @@
     return true;
 }
 
 inline bool RenderObject::isBeforeOrAfterContent() const
 {
     return isBeforeContent() || isAfterContent();
 }
 
 inline void RenderObject::setNeedsLayout(MarkingBehavior markParents, SubtreeLayoutScope* layouter)
 {
+#ifndef NDEBUG
+    checkNotInPartialLayout();
+#endif
     ASSERT(!isSetNeedsLayoutForbidden());
     bool alreadyNeededLayout = m_bitfields.needsLayout();
     m_bitfields.setNeedsLayout(true);
     if (!alreadyNeededLayout) {
         if (markParents == MarkContainingBlockChain && (!layouter || layouter->root() != this))
             markContainingBlocksForLayout(true, 0, layouter);
         if (hasLayer())
             setLayerNeedsFullRepaint();
     }
 }
 
 inline void RenderObject::clearNeedsLayout()
 {
+#ifndef NDEBUG
+    checkNotInPartialLayout();
+#endif
     m_bitfields.setNeedsLayout(false);
     setEverHadLayout(true);
     setPosChildNeedsLayout(false);
     setNeedsSimplifiedNormalFlowLayout(false);
     setNormalChildNeedsLayout(false);
     setNeedsPositionedMovementLayout(false);
     setAncestorLineBoxDirty(false);
 #ifndef NDEBUG
     checkBlockPositionedObjectsNeedLayout();
 #endif
@@ skipping 124 matching lines @@
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const WebCore::RenderObject*);
 void showLineTree(const WebCore::RenderObject*);
 void showRenderTree(const WebCore::RenderObject* object1);
 // We don't make object2 an optional parameter so that showRenderTree
 // can be called from gdb easily.
 void showRenderTree(const WebCore::RenderObject* object1, const WebCore::RenderObject* object2);
 #endif
 
 #endif // RenderObject_h