Need to roll back the multicol machinery state when re-laying out a block child.

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

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 23 matching lines @@
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/paint/PaintLayerFragment.h"
 #include "wtf/ListHashSet.h"
 
 namespace blink {
 
 class LayoutMultiColumnSet;
 
 typedef ListHashSet<LayoutMultiColumnSet*> LayoutMultiColumnSetList;
 
+// Layout state for multicol. To be stored when laying out a block child, so that we can roll back
+// to the initial state if we need to re-lay out said block child.
+class MultiColumnLayoutState {
+    friend class LayoutMultiColumnFlowThread;
+
+public:
+    MultiColumnLayoutState() : m_columnSet(nullptr) { }
+
+private:
+    explicit MultiColumnLayoutState(LayoutMultiColumnSet* columnSet) : m_columnSet(columnSet) { }
+    LayoutMultiColumnSet* columnSet() const { return m_columnSet; }
+
+    LayoutMultiColumnSet* m_columnSet;
+};
+
 // LayoutFlowThread is used to collect all the layout objects that participate in a flow thread. It
 // will also help in doing the layout. However, it will not layout directly to screen. Instead,
 // LayoutMultiColumnSet objects will redirect their paint and nodeAtPoint methods to this
 // object. Each LayoutMultiColumnSet will actually be a viewPort of the LayoutFlowThread.
 class CORE_EXPORT LayoutFlowThread: public LayoutBlockFlow {
 public:
     LayoutFlowThread();
     ~LayoutFlowThread() override { }
 
     bool isLayoutFlowThread() const final { return true; }
@@ skipping 27 matching lines @@
     bool hasValidColumnSetInfo() const { return !m_columnSetsInvalidated && !m_multiColumnSetList.isEmpty(); }
 
     bool mapToVisualRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, VisualRectFlags = DefaultVisualRectFlags) const override;
 
     LayoutUnit pageLogicalHeightForOffset(LayoutUnit);
     LayoutUnit pageRemainingLogicalHeightForOffset(LayoutUnit, PageBoundaryRule);
 
     virtual void contentWasLaidOut(LayoutUnit logicalBottomInFlowThreadAfterPagination) = 0;
     virtual bool canSkipLayout(const LayoutBox&) const = 0;
 
+    virtual MultiColumnLayoutState multiColumnLayoutState() const = 0;
+    virtual void restoreMultiColumnLayoutState(const MultiColumnLayoutState&) = 0;
+
     // Find and return the next logical top after |flowThreadOffset| that can fit unbreakable
     // content as tall as |contentLogicalHeight|. |flowThreadOffset| is expected to be at the exact
     // top of a column that's known to not have enough space for |contentLogicalHeight|. This method
     // is called when the current column is too short to fit the content, in the hope that there
     // exists one that's tall enough further ahead. If no such column can be found,
     // |flowThreadOffset| will be returned.
     LayoutUnit nextLogicalTopForUnbreakableContent(LayoutUnit flowThreadOffset, LayoutUnit contentLogicalHeight) const;
 
     virtual bool isPageLogicalHeightKnown() const { return true; }
     bool pageLogicalSizeChanged() const { return m_pageLogicalSizeChanged; }
@@ skipping 49 matching lines @@
 // These structures are used by PODIntervalTree for debugging.
 #ifndef NDEBUG
 template <> struct ValueToString<LayoutMultiColumnSet*> {
     static String toString(const LayoutMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // LayoutFlowThread_h