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

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index 8c150d19f17d4ca1257f7ff3f20a7c7360971482..d41a5bb3d2c9f88e0e9beb85c4aa459ea6036cbb 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -46,6 +46,7 @@
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderDeprecatedFlexibleBox.h"
 #include "core/rendering/RenderFlexibleBox.h"
+#include "core/rendering/RenderFlowThread.h"
 #include "core/rendering/RenderGeometryMap.h"
 #include "core/rendering/RenderGrid.h"
 #include "core/rendering/RenderInline.h"
@@ -216,6 +217,11 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
 
     updateShapeOutsideInfoAfterStyleChange(*style(), oldStyle);
     updateGridPositionAfterStyleChange(oldStyle);
+
+    if (RenderFlowThread* flowThread = flowThreadContainingBlock()) {
+        if (flowThread != this)
+            flowThread->flowThreadDescendantStyleDidChange(this);
+    }
 }
 
 void RenderBox::updateShapeOutsideInfoAfterStyleChange(const RenderStyle& style, const RenderStyle* oldStyle)
@@ -1480,7 +1486,11 @@ LayoutUnit RenderBox::containingBlockLogicalWidthForContent() const
     if (hasOverrideContainingBlockLogicalWidth())
         return overrideContainingBlockContentLogicalWidth();
 
-    RenderBlock* cb = containingBlock();
+    RenderBlock* cb;
+    if (isColumnSpanAll())
+        cb = flowThreadContainingBlock()->containingBlock();
+    else
+        cb = containingBlock();
     return cb->availableLogicalWidth();
 }
 
@@ -1489,7 +1499,11 @@ LayoutUnit RenderBox::containingBlockLogicalHeightForContent(AvailableLogicalHei
     if (hasOverrideContainingBlockLogicalHeight())
         return overrideContainingBlockContentLogicalHeight();
 
-    RenderBlock* cb = containingBlock();
+    RenderBlock* cb;
+    if (isColumnSpanAll())
+        cb = flowThreadContainingBlock()->containingBlock();
+    else
+        cb = containingBlock();
     return cb->availableLogicalHeight(heightType);
 }
 
@@ -2111,7 +2125,7 @@ bool RenderBox::autoWidthShouldFitContent() const
 void RenderBox::computeMarginsForDirection(MarginDirection flowDirection, const RenderBlock* containingBlock, LayoutUnit containerWidth, LayoutUnit childWidth, LayoutUnit& marginStart, LayoutUnit& marginEnd, Length marginStartLength, Length marginEndLength) const
 {
     if (flowDirection == BlockDirection || isFloating() || isInline()) {
-        if (isTableCell() && flowDirection == BlockDirection) {
+        if ((isColumnSpanAll() || isTableCell()) && flowDirection == BlockDirection) {
             // FIXME: Not right if we allow cells to have different directionality than the table. If we do allow this, though,
             // we may just do it with an extra anonymous block inside the cell.
             marginStart = 0;
@@ -4179,7 +4193,11 @@ bool RenderBox::hasUnsplittableScrollingOverflow() const
 
 bool RenderBox::isUnsplittableForPagination() const
 {
-    return isReplaced() || hasUnsplittableScrollingOverflow() || (parent() && isWritingModeRoot());
+    // FIXME: column spanners are only unsplittable (or rather: they do not participate in
+    // fragmentation) in their nearest ancestor multicol container. If there are additional
+    // fragmentation contexts further up in the tree, spanners still need to take those into
+    // account.
+    return isReplaced() || hasUnsplittableScrollingOverflow() || (parent() && isWritingModeRoot()) || isColumnSpanAll();
 }
 
 LayoutUnit RenderBox::lineHeight(bool /*firstLine*/, LineDirectionMode direction, LinePositionMode /*linePositionMode*/) const