[New Multicolumn] Layout support for column-span:all.

Source/core/rendering/RenderBlockFlow.cpp

Index: Source/core/rendering/RenderBlockFlow.cpp
diff --git a/Source/core/rendering/RenderBlockFlow.cpp b/Source/core/rendering/RenderBlockFlow.cpp
index 391f2db532359af17708f47fd591a0dab7fbd63b..1d7d6918238ef36b82bf185d1ada884ae0b19c3a 100644
--- a/Source/core/rendering/RenderBlockFlow.cpp
+++ b/Source/core/rendering/RenderBlockFlow.cpp
@@ -683,6 +683,11 @@ void RenderBlockFlow::layoutBlockChild(RenderBox& child, MarginInfo& marginInfo,
         if (newHeight != size().height())
             setLogicalHeight(newHeight);
     }
+
+    if (child.isRenderMultiColumnSpannerPlaceholder()) {
+        // The actual column-span:all element is positioned by this placeholder child.
+        positionSpannerDescendant(toRenderMultiColumnSpannerPlaceholder(child));
+    }
 }
 
 LayoutUnit RenderBlockFlow::adjustBlockChildForPagination(LayoutUnit logicalTopAfterClear, LayoutUnit estimateWithoutPagination, RenderBox& child, bool atBeforeSideOfBlock)
@@ -1060,7 +1065,10 @@ void RenderBlockFlow::layoutBlockChildren(bool relayoutChildren, SubtreeLayoutSc
         }
         if (child->isColumnSpanAll()) {
             // This is not the containing block of the spanner. The spanner's placeholder will lay
-            // it out in due course.
+            // it out in due course. For now we just need to consult our flow thread, so that the
+            // columns (if any) preceding and following the spanner are laid out correctly.
+            LayoutUnit adjustment = flowThreadContainingBlock()->skipColumnSpanner(child, offsetFromLogicalTopOfFirstPage() + logicalHeight());
+            setLogicalHeight(logicalHeight() + adjustment);
             continue;
         }
 
@@ -2972,6 +2980,15 @@ void RenderBlockFlow::setPaginationStrut(LayoutUnit strut)
     m_rareData->m_paginationStrut = strut;
 }
 
+void RenderBlockFlow::positionSpannerDescendant(RenderMultiColumnSpannerPlaceholder& child)
+{
+    RenderBox& spanner = *child.rendererInFlowThread();
+    // FIXME: |spanner| is a descendant, but never a direct child, so the names here are bad, if
+    // nothing else.
+    setLogicalTopForChild(spanner, child.logicalTop());
+    determineLogicalLeftPositionForChild(spanner);
+}
+
 bool RenderBlockFlow::avoidsFloats() const
 {
     // Floats can't intrude into our box if we have a non-auto column count or width.