Consistent pagination strut propagation policies.

third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 4106 matching lines @@
     return false;
   }
   const LayoutBlock* containingBlock = this->containingBlock();
   if (!containingBlock || !containingBlock->isLayoutBlockFlow())
     return false;
   const LayoutBlockFlow* containingBlockFlow =
       toLayoutBlockFlow(containingBlock);
   // If children are inline, allow the strut. We are probably a float.
   if (containingBlockFlow->childrenInline())
     return true;
-  // If this isn't the first in-flow object, there's a break opportunity before
-  // us, which means that we can allow the strut.
-  if (previousInFlowSiblingBox())
-    return true;
+  for (LayoutBox* sibling = previousSiblingBox(); sibling;
+       sibling = sibling->previousSiblingBox()) {
+    // What happens on the other side of a spanner is none of our concern, so
+    // stop here. Since there's no in-flow box between the previous spanner and
+    // us, there's no class A break point in front of us. We cannot even
+    // re-propagate pagination struts to our containing block, since the
+    // containing block starts in a different column row.
+    if (sibling->isColumnSpanAll())
+      return false;
+    // If this isn't the first in-flow object, there's a break opportunity
+    // before us, which means that we can allow the strut.
+    if (!sibling->isFloatingOrOutOfFlowPositioned())
+      return true;
+  }
   // This is a first in-flow child. We'll still allow the strut if it can be
   // re-propagated to our containing block.
   return containingBlockFlow->allowsPaginationStrut();
 }
 
 void LayoutBlockFlow::setPaginationStrutPropagatedFromChild(LayoutUnit strut) {
   strut = std::max(strut, LayoutUnit());
   if (!m_rareData) {
     if (!strut)
       return;
@@ skipping 464 matching lines @@
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(
     PaintInvalidationReason invalidationReason) const {
   BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
       invalidationReason);
 }
 
 }  // namespace blink