Incorrect invalidation on Google Forum

Source/core/rendering/RenderBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. 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
  * License as published by the Free Software Foundation; either
@@ skipping 1473 matching lines @@
     } else {
         for (RenderBox* box = firstChildBox(); box; box = box->nextSiblingBox()) {
             if (!box->isOutOfFlowPositioned())
                 box->layoutIfNeeded();
         }
     }
 }
 
 bool RenderBlock::simplifiedLayout()
 {
-    if ((!posChildNeedsLayout() && !needsSimplifiedNormalFlowLayout()) || normalChildNeedsLayout() || selfNeedsLayout())
+    // Check if we need to do a full layout.
+    if (normalChildNeedsLayout() || selfNeedsLayout())
+        return false;
+
+    // Check that we actually need to do a simplified layout.
+    if (!posChildNeedsLayout() && !(needsSimplifiedNormalFlowLayout() || needsPositionedMovementLayout()))
         return false;
 
 
     {
         // LayoutStateMaintainer needs this deliberate scope to pop before repaint
         LayoutStateMaintainer statePusher(*this, locationOffset());
 
         if (needsPositionedMovementLayout() && !tryLayoutDoingPositionedMovementOnly())
             return false;
 
         FastTextAutosizer::LayoutScope fastTextAutosizerLayoutScope(this);
 
         // Lay out positioned descendants or objects that just need to recompute overflow.
         if (needsSimplifiedNormalFlowLayout())
             simplifiedNormalFlowLayout();
 
         // Make sure a forced break is applied after the content if we are a flow thread in a simplified layout.
         // This ensures the size information is correctly computed for the last auto-height region receiving content.
         if (isRenderFlowThread())
             toRenderFlowThread(this)->applyBreakAfterContent(clientLogicalBottom());
 
         // Lay out our positioned objects if our positioned child bit is set.
         // Also, if an absolute position element inside a relative positioned container moves, and the absolute element has a fixed position
         // child, neither the fixed element nor its container learn of the movement since posChildNeedsLayout() is only marked as far as the
         // relative positioned container. So if we can have fixed pos objects in our positioned objects list check if any of them
         // are statically positioned and thus need to move with their absolute ancestors.
         bool canContainFixedPosObjects = canContainFixedPositionObjects();
-        if (posChildNeedsLayout() || canContainFixedPosObjects)
-            layoutPositionedObjects(false, !posChildNeedsLayout() && canContainFixedPosObjects ? LayoutOnlyFixedPositionedObjects : DefaultLayout);
+        if (posChildNeedsLayout() || needsPositionedMovementLayout() || canContainFixedPosObjects)
+            layoutPositionedObjects(false, needsPositionedMovementLayout() ? ForcedLayoutAfterContainingBlockMoved : (!posChildNeedsLayout() && canContainFixedPosObjects ? LayoutOnlyFixedPositionedObjects : DefaultLayout));
 
         // Recompute our overflow information.
         // FIXME: We could do better here by computing a temporary overflow object from layoutPositionedObjects and only
         // updating our overflow if we either used to have overflow or if the new temporary object has overflow.
         // For now just always recompute overflow. This is no worse performance-wise than the old code that called rightmostPosition and
         // lowestPosition on every relayout so it's not a regression.
         // computeOverflow expects the bottom edge before we clamp our height. Since this information isn't available during
         // simplifiedLayout, we cache the value in m_overflow.
         LayoutUnit oldClientAfterEdge = hasRenderOverflow() ? m_overflow->layoutClientAfterEdge() : clientLogicalBottom();
         computeOverflow(oldClientAfterEdge, true);
@@ skipping 87 matching lines @@
         if (relayoutChildren || (r->style()->hasStaticBlockPosition(isHorizontalWritingMode()) && r->parent() != this))
             layoutScope.setChildNeedsLayout(r);
 
         // If relayoutChildren is set and the child has percentage padding or an embedded content box, we also need to invalidate the childs pref widths.
         if (relayoutChildren && r->needsPreferredWidthsRecalculation())
             r->setPreferredLogicalWidthsDirty(MarkOnlyThis);
 
         if (!r->needsLayout())
             r->markForPaginationRelayoutIfNeeded(layoutScope);
 
-        // We don't have to do a full layout.  We just have to update our position. Try that first. If we have shrink-to-fit width
-        // and we hit the available width constraint, the layoutIfNeeded() will catch it and do a full layout.
-        if (r->needsPositionedMovementLayoutOnly() && r->tryLayoutDoingPositionedMovementOnly())
-            r->clearNeedsLayout();
-
         // If we are paginated or in a line grid, go ahead and compute a vertical position for our object now.
         // If it's wrong we'll lay out again.
         LayoutUnit oldLogicalTop = 0;
         bool needsBlockDirectionLocationSetBeforeLayout = r->needsLayout() && view()->layoutState()->needsBlockDirectionLocationSetBeforeLayout();
         if (needsBlockDirectionLocationSetBeforeLayout) {
             if (isHorizontalWritingMode() == r->isHorizontalWritingMode())
                 r->updateLogicalHeight();
             else
                 r->updateLogicalWidth();
             oldLogicalTop = logicalTopForChild(r);
@@ skipping 3308 matching lines @@
 void RenderBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     showRenderObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace WebCore