Region based multicol: support explicit column breaks

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 59e457e6026438e3d2a9117689e348184fff7a8f..7d264c98a423bb936f93a23ca94c201e841552c1 100644
--- a/Source/core/rendering/RenderBlockFlow.cpp
+++ b/Source/core/rendering/RenderBlockFlow.cpp
@@ -1574,15 +1574,21 @@ bool RenderBlockFlow::mustSeparateMarginAfterForChild(const RenderBox* child) co
 LayoutUnit RenderBlockFlow::applyBeforeBreak(RenderBox* child, LayoutUnit logicalOffset)
 {
     // FIXME: Add page break checking here when we support printing.
-    bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns();
-    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
+    bool isInsideMulticolFlowThread = flowThread && !flowThread->isRenderNamedFlowThread();
+    bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
+    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     bool checkRegionBreaks = flowThread && flowThread->isRenderNamedFlowThread();
-    bool checkBeforeAlways = (checkColumnBreaks && child->style()->columnBreakBefore() == PBALWAYS) || (checkPageBreaks && child->style()->pageBreakBefore() == PBALWAYS)
+    bool checkBeforeAlways = (checkColumnBreaks && child->style()->columnBreakBefore() == PBALWAYS)
+        || (checkPageBreaks && child->style()->pageBreakBefore() == PBALWAYS)
         || (checkRegionBreaks && child->style()->regionBreakBefore() == PBALWAYS);
     if (checkBeforeAlways && inNormalFlow(child) && hasNextPage(logicalOffset, IncludePageBoundary)) {
-        if (checkColumnBreaks)
-            view()->layoutState()->addForcedColumnBreak(child, logicalOffset);
+        if (checkColumnBreaks) {
+            if (isInsideMulticolFlowThread)
+                checkRegionBreaks = true;
+            else
+                view()->layoutState()->addForcedColumnBreak(child, logicalOffset);
+        }
         if (checkRegionBreaks) {
             LayoutUnit offsetBreakAdjustment = 0;
             if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset, child, true, &offsetBreakAdjustment))
@@ -1596,11 +1602,13 @@ LayoutUnit RenderBlockFlow::applyBeforeBreak(RenderBox* child, LayoutUnit logica
 LayoutUnit RenderBlockFlow::applyAfterBreak(RenderBox* child, LayoutUnit logicalOffset, MarginInfo& marginInfo)
 {
     // FIXME: Add page break checking here when we support printing.
-    bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns();
-    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
+    bool isInsideMulticolFlowThread = flowThread && !flowThread->isRenderNamedFlowThread();
+    bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
+    bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     bool checkRegionBreaks = flowThread && flowThread->isRenderNamedFlowThread();
-    bool checkAfterAlways = (checkColumnBreaks && child->style()->columnBreakAfter() == PBALWAYS) || (checkPageBreaks && child->style()->pageBreakAfter() == PBALWAYS)
+    bool checkAfterAlways = (checkColumnBreaks && child->style()->columnBreakAfter() == PBALWAYS)
+        || (checkPageBreaks && child->style()->pageBreakAfter() == PBALWAYS)
         || (checkRegionBreaks && child->style()->regionBreakAfter() == PBALWAYS);
     if (checkAfterAlways && inNormalFlow(child) && hasNextPage(logicalOffset, IncludePageBoundary)) {
         LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();
@@ -1608,8 +1616,12 @@ LayoutUnit RenderBlockFlow::applyAfterBreak(RenderBox* child, LayoutUnit logical
         // So our margin doesn't participate in the next collapsing steps.
         marginInfo.clearMargin();
 
-        if (checkColumnBreaks)
-            view()->layoutState()->addForcedColumnBreak(child, logicalOffset);
+        if (checkColumnBreaks) {
+            if (isInsideMulticolFlowThread)
+                checkRegionBreaks = true;
+            else
+                view()->layoutState()->addForcedColumnBreak(child, logicalOffset);
+        }
         if (checkRegionBreaks) {
             LayoutUnit offsetBreakAdjustment = 0;
             if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset + marginOffset, child, false, &offsetBreakAdjustment))