Don't leave stale pointers into m_grid

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index b1f23c92913d273a20075b404deb973a7fdd860e..2615bd449fdf42189199df15141bfafc15359408 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -49,6 +49,7 @@
 #include "core/rendering/RenderDeprecatedFlexibleBox.h"
 #include "core/rendering/RenderFlexibleBox.h"
 #include "core/rendering/RenderFlowThread.h"
+#include "core/rendering/RenderGrid.h"
 #include "core/rendering/RenderInline.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderMarquee.h"
@@ -1052,6 +1053,10 @@ void RenderBlock::removeLeftoverAnonymousBlock(RenderBlock* child)
     // Remove all the information in the flow thread associated with the leftover anonymous block.
     child->removeFromRenderFlowThread();
 
+    // RenderGrid keeps track of its children, we must notify it about changes in the tree.
+    if (child->parent()->isRenderGrid())
+        toRenderGrid(child->parent())->dirtyGrid();
+
     child->setParent(0);
     child->setPreviousSibling(0);
     child->setNextSibling(0);