[New Multicolumn] Add support for column-span:all

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 a029d1b940fb66423676f2e7b4b5007cd26ed3da..ab69c91daddb00f0bfeec943d1a907dac857d243 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -1073,9 +1073,6 @@ void RenderBlock::removeLeftoverAnonymousBlock(RenderBlock* child)
     child->children()->setFirstChild(0);
     child->m_next = nullptr;
 
-    // Remove all the information in the flow thread associated with the leftover anonymous block.
-    child->removeFromRenderFlowThread();

[Julien - ping for review, 2014/09/30 00:39:32]

Are we sure we don't insert children into the flow-thread that needs to be
cleaned up now?

[mstensho (USE GERRIT), 2014/09/30 20:20:28]

This is an anonymous block, and just became childless. Anonymous blocks don't do
anything special inside a flow thread. The real reason why I had to remove this,
though, is that it calls removeFromRenderFlowThread() while being "half-dead" -
or at least half-detached. This confused flowThreadDescendantWillBeRemoved(),
since that method attempts to walk the subtree.

removeFromRenderFlowThread() is still called from willBeRemovedFromTree(), and
that should be sufficient. It's a pity that removeLeftoverAnonymousBlock() needs
to tear down its child single-handedly, but I'm sure there's a reason for that.
Might as well be related to crbug.com/417556 for all I know. :)

-
     // RenderGrid keeps track of its children, we must notify it about changes in the tree.
     if (child->parent()->isRenderGrid())
         toRenderGrid(child->parent())->dirtyGrid();
@@ -1525,7 +1522,7 @@ void RenderBlock::addVisualOverflowFromTheme()
 bool RenderBlock::createsBlockFormattingContext() const
 {
     return isInlineBlockOrInlineTable() || isFloatingOrOutOfFlowPositioned() || hasOverflowClip() || isFlexItemIncludingDeprecated()
-        || style()->specifiesColumns() || isRenderFlowThread() || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElement() || style()->columnSpan();
+        || style()->specifiesColumns() || isRenderFlowThread() || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElement() || (document().regionBasedColumnsEnabled() ? isColumnSpanAll() : style()->columnSpan());
 }
 
 void RenderBlock::updateBlockChildDirtyBitsBeforeLayout(bool relayoutChildren, RenderBox* child)