Fix table cell background painting

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

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 58 matching lines @@
 
     const LayoutObjectChildList* children() const { return &m_children; }
     LayoutObjectChildList* children() { return &m_children; }
 
     void clearPreferredLogicalWidthsDirtyBits();
 
     // The 'span' attribute in HTML.
     // For CSS table columns or colgroups, this is always 1.
     unsigned span() const { return m_span; }
 
-    bool isTableColumnGroupWithColumnChildren() { return firstChild(); }
+    bool isTableColumnGroupWithColumnChildren() const { return firstChild(); }
     bool isTableColumn() const { return style()->display() == TABLE_COLUMN; }
     bool isTableColumnGroup() const { return style()->display() == TABLE_COLUMN_GROUP; }
 
     LayoutTableCol* enclosingColumnGroup() const;
+    LayoutTableCol* lastColumnInGroup() const;
 
     // Returns the next column or column-group.
     LayoutTableCol* nextColumn() const;
 
     const BorderValue& borderAdjoiningCellStartBorder(const LayoutTableCell*) const;
     const BorderValue& borderAdjoiningCellEndBorder(const LayoutTableCell*) const;
     const BorderValue& borderAdjoiningCellBefore(const LayoutTableCell*) const;
     const BorderValue& borderAdjoiningCellAfter(const LayoutTableCell*) const;
 
     const char* name() const override { return "LayoutTableCol"; }
 
+    // Returns col/colgroup table-relative position.
+    // <col> elements need to provide absoluteColumnIndex.

[Xianzhu, 2016/03/28 00:44:42]

Can you rephrase the above sentence?

[atotic1, 2016/03/29 17:05:16]

Done.

+    // This is because <col> element with span N is treated for display as
+    // N <col> elements with span 1. It does not make sense to talk
+    // about visual <col> position, only about <col> position at
+    // particular absolute column.

[Xianzhu, 2016/03/28 00:44:42]

I think you can omit the above comments.

[atotic1, 2016/03/29 17:05:16]

Moved it into .cpp. The comment describes a non-intuitive aspect of table spec.

+    LayoutRect positionByCellSpan(unsigned absoluteColumnIndex) const;
+
+    // Return indexes to all columns inside this element.
+    // Can return vector with size 0 if LayoutTableCol is out of range.
+    // <col> element can return size() > 1 if it spans multiple columns
+    // <colgroup> element can return any size.
+    Vector<unsigned> getEffectiveColumnIndexes() const;
+
 private:
     LayoutObjectChildList* virtualChildren() override { return children(); }
     const LayoutObjectChildList* virtualChildren() const override { return children(); }
 
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectLayoutTableCol || LayoutBox::isOfType(type); }
     void updateFromElement() override;
     void computePreferredLogicalWidths() override { ASSERT_NOT_REACHED(); }
 
     void insertedIntoTree() override;
     void willBeRemovedFromTree() override;
@@ skipping 11 matching lines @@
 
     LayoutObjectChildList m_children;
     unsigned m_span;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutTableCol, isLayoutTableCol());
 
 } // namespace blink
 
 #endif