[New Multicolumn] Add 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 068627320dad05554a93bd69b39d3ba7dbdbe420..d29ef66cf605bad310695b1f7db411ef31d66297 100644
--- a/Source/core/rendering/RenderBlockFlow.cpp
+++ b/Source/core/rendering/RenderBlockFlow.cpp
@@ -552,6 +552,20 @@ void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo,
 {
     LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
     LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();
+    bool childIsColumnSpanner = child->isColumnSpanAll();
+
+    if (childIsColumnSpanner) {

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

Nit: This looks like it should be a RAII so that we enter / leave are always
paired.

+        // Margins of a column spanner cannot collapse with anything. Block direction margins on
+        // spanners will be ignored here, inside flow thread layout. Instead they'll be added around
+        // the RenderMultiColumnSpannerSet. Now skip past the pending margin that belongs to the
+        // columns.
+        setLogicalHeight(logicalHeight() + marginInfo.margin());
+        marginInfo.clearMargin();
+        LayoutUnit adjustment = flowThreadContainingBlock()->enterColumnSpanner(child, logicalHeight());
+        // A spanner needs to start at an exact column boundary inside the flow thread, so that it
+        // doesn't bleed into a preceding column. That's what the adjustment is about.
+        setLogicalHeight(logicalHeight() + adjustment);
+    }
 
     // The child is a normal flow object. Compute the margins we will use for collapsing now.
     child->computeAndSetBlockDirectionMargins(this);
@@ -687,6 +701,11 @@ void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo,
         LayoutUnit newHeight = applyAfterBreak(child, logicalHeight(), marginInfo);
         if (newHeight != height())
             setLogicalHeight(newHeight);
+
+        if (childIsColumnSpanner) {
+            flowThreadContainingBlock()->leaveColumnSpanner(child, logicalHeight());
+            ASSERT(!marginInfo.margin());
+        }
     }
 }
 
@@ -1285,7 +1304,7 @@ LayoutUnit RenderBlockFlow::collapseMargins(RenderBox* child, MarginInfo& margin
     // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
     // collapsed into the page edge.
     LayoutState* layoutState = view()->layoutState();
-    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop) {
+    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop && !child->isColumnSpanAll()) {
         LayoutUnit oldLogicalTop = logicalTop;
         logicalTop = std::min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
         setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
@@ -1501,7 +1520,7 @@ LayoutUnit RenderBlockFlow::estimateLogicalTopPosition(RenderBox* child, const M
     // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
     // page.
     LayoutState* layoutState = view()->layoutState();
-    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight())
+    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight() && !child->isColumnSpanAll())
         logicalTopEstimate = std::min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));
 
     logicalTopEstimate += getClearDelta(child, logicalTopEstimate);