LayoutBlockFlow: rename paginationStrut to paginationStrutPropagatedFromChild.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003-2013 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * 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
@@ skipping 200 matching lines @@
         LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight,
         const PaintInfo* = nullptr, ClipScope* = nullptr) const;
     GapRects inlineSelectionGaps(const LayoutBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
         LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo*) const;
     GapRects blockSelectionGaps(const LayoutBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
         LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo*) const;
     LayoutRect blockSelectionGap(const LayoutBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
         LayoutUnit lastLogicalTop, LayoutUnit lastLogicalLeft, LayoutUnit lastLogicalRight, LayoutUnit logicalBottom, const PaintInfo*) const;
 
     bool allowsPaginationStrut() const;
-    LayoutUnit paginationStrut() const { return m_rareData ? m_rareData->m_paginationStrut : LayoutUnit(); }
-    void setPaginationStrut(LayoutUnit);
+    // Pagination strut caused by the first line or child block inside this block-level object.
+    //
+    // When the first piece of content (first child block or line) inside an object wants to insert
+    // a soft page or column break, rather than setting a pagination strut on itself it normally
+    // propagates the strut to its containing block (|this|), as long as our implementation can
+    // handle it. The idea is that we want to push the entire object to the next page or column
+    // along with the child content that caused the break, instead of leaving unusable space at the
+    // beginning of the object at the end of one column or page and just push the first line or
+    // block to the next column or page. That would waste space in the container for no good
+    // reason, and it would also be a spec violation, since there is no break opportunity defined
+    // between the content logical top of an object and its first child or line (only *between*
+    // blocks or lines).
+    LayoutUnit paginationStrutPropagatedFromChild() const { return m_rareData ? m_rareData->m_paginationStrutPropagatedFromChild : LayoutUnit(); }
+    void setPaginationStrutPropagatedFromChild(LayoutUnit);
 
     void positionSpannerDescendant(LayoutMultiColumnSpannerPlaceholder& child);
 
     bool avoidsFloats() const override;
 
     using LayoutBoxModelObject::moveChildrenTo;
     void moveChildrenTo(LayoutBoxModelObject* toBoxModelObject, LayoutObject* startChild, LayoutObject* endChild, LayoutObject* beforeChild, bool fullRemoveInsert = false) override;
 
     LayoutUnit xPositionForFloatIncludingMargin(const FloatingObject& child) const
     {
@@ skipping 182 matching lines @@
         LayoutUnit m_negativeMarginAfter;
     };
     MarginValues marginValuesForChild(LayoutBox& child) const;
 
     // Allocated only when some of these fields have non-default values
     struct LayoutBlockFlowRareData {
         WTF_MAKE_NONCOPYABLE(LayoutBlockFlowRareData); WTF_MAKE_FAST_ALLOCATED(LayoutBlockFlowRareData);
     public:
         LayoutBlockFlowRareData(const LayoutBlockFlow* block)
             : m_margins(positiveMarginBeforeDefault(block), negativeMarginBeforeDefault(block), positiveMarginAfterDefault(block), negativeMarginAfterDefault(block))
-            , m_paginationStrut(0)
             , m_multiColumnFlowThread(nullptr)
             , m_lineBreakToAvoidWidow(-1)
             , m_didBreakAtLineToAvoidWidow(false)
             , m_discardMarginBefore(false)
             , m_discardMarginAfter(false)
         {
         }
 
         static LayoutUnit positiveMarginBeforeDefault(const LayoutBlockFlow* block)
         {
             return std::max<LayoutUnit>(block->marginBefore(), 0);
         }
         static LayoutUnit negativeMarginBeforeDefault(const LayoutBlockFlow* block)
         {
             return std::max<LayoutUnit>(-block->marginBefore(), 0);
         }
         static LayoutUnit positiveMarginAfterDefault(const LayoutBlockFlow* block)
         {
             return std::max<LayoutUnit>(block->marginAfter(), 0);
         }
         static LayoutUnit negativeMarginAfterDefault(const LayoutBlockFlow* block)
         {
             return std::max<LayoutUnit>(-block->marginAfter(), 0);
         }
 
         MarginValues m_margins;
-        LayoutUnit m_paginationStrut;
+        LayoutUnit m_paginationStrutPropagatedFromChild;
 
         LayoutMultiColumnFlowThread* m_multiColumnFlowThread;
 
         int m_lineBreakToAvoidWidow;
         bool m_didBreakAtLineToAvoidWidow : 1;
         bool m_discardMarginBefore : 1;
         bool m_discardMarginAfter : 1;
     };
 
     const FloatingObjects* floatingObjects() const { return m_floatingObjects.get(); }
@@ skipping 105 matching lines @@
 
 // END METHODS DEFINED IN LayoutBlockFlowLine
 
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlockFlow, isLayoutBlockFlow());
 
 } // namespace blink
 
 #endif // LayoutBlockFlow_h