Fix scroll origin, overflow rects, and coordinate flipping for flexbox.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 362 matching lines @@
     LayoutUnit logicalLeftLayoutOverflow() const { return style()->isHorizontalWritingMode() ? layoutOverflowRect().x() : layoutOverflowRect().y(); }
     LayoutUnit logicalRightLayoutOverflow() const { return style()->isHorizontalWritingMode() ? layoutOverflowRect().maxX() : layoutOverflowRect().maxY(); }
 
     LayoutRect visualOverflowRect() const override;
     LayoutUnit logicalLeftVisualOverflow() const { return style()->isHorizontalWritingMode() ? visualOverflowRect().x() : visualOverflowRect().y(); }
     LayoutUnit logicalRightVisualOverflow() const { return style()->isHorizontalWritingMode() ? visualOverflowRect().maxX() : visualOverflowRect().maxY(); }
 
     LayoutRect selfVisualOverflowRect() const { return m_overflow ? m_overflow->selfVisualOverflowRect() : borderBoxRect(); }
     LayoutRect contentsVisualOverflowRect() const { return m_overflow ? m_overflow->contentsVisualOverflowRect() : LayoutRect(); }
 
+    // These methods don't mean the box *actually* has top/left overflow.  They mean that

[cbiesinger, 2016/05/11 19:44:00]

maybe rename to canOverflowTo{Top,Left}?

+    // *if* the box overflows, it will overflow to the top/left rather than the bottom/right.
+    // This happens when child content is laid out right-to-left (e.g. direction:rtl) or
+    // or bottom-to-top (e.g. direction:rtl writing-mode:vertical-rl).
+    virtual bool hasTopOverflow() const;

[leviw_travelin_and_unemployed, 2016/05/10 17:52:42]

The name still strikes me as confusing (seems like if we called them
overflowFlowsLeft/Top or something you may not need as much comment), but I
won't block an otherwise amazing patch over this.

+    virtual bool hasLeftOverflow() const;
+
     void addLayoutOverflow(const LayoutRect&);
     void addSelfVisualOverflow(const LayoutRect&);
     void addContentsVisualOverflow(const LayoutRect&);
 
     void addVisualEffectOverflow();
     LayoutRectOutsets computeVisualEffectOverflowOutsets() const;
     void addOverflowFromChild(LayoutBox* child) { addOverflowFromChild(child, child->locationOffset()); }
     void addOverflowFromChild(LayoutBox* child, const LayoutSize& delta);
     void clearLayoutOverflow();
     void clearAllOverflows() { m_overflow.clear(); }
@@ skipping 471 matching lines @@
     LayoutRect visualOverflowRectForPropagation(const ComputedStyle&) const;
     LayoutRect logicalLayoutOverflowRectForPropagation(const ComputedStyle&) const;
     LayoutRect layoutOverflowRectForPropagation(const ComputedStyle&) const;
 
     bool hasOverflowModel() const { return m_overflow.get(); }
     bool hasSelfVisualOverflow() const { return m_overflow && !borderBoxRect().contains(m_overflow->selfVisualOverflowRect()); }
     bool hasVisualOverflow() const { return m_overflow && !borderBoxRect().contains(visualOverflowRect()); }
 
     virtual bool needsPreferredWidthsRecalculation() const;
 
+    // See README.md for an explanation of scroll origin.
+    virtual IntSize originAdjustmentForScrollbars() const;
     IntSize scrolledContentOffset() const;
 
     // Maps a rect in scrolling contents space to box space and apply overflow clip if needed.
     // Returns true if no clipping applied or the rect actually intersects the clipping region.
     // If edgeInclusive is true, then this method may return true even
     // if the resulting rect has zero area.
     bool mapScrollingContentsRectToBoxSpace(LayoutRect&, ApplyOverflowClipFlag, VisualRectFlags = DefaultVisualRectFlags) const;
 
     virtual bool hasRelativeLogicalWidth() const;
     virtual bool hasRelativeLogicalHeight() const;
@@ skipping 295 matching lines @@
         || breakValue == BreakLeft
         || breakValue == BreakPage
         || breakValue == BreakRecto
         || breakValue == BreakRight
         || breakValue == BreakVerso;
 }
 
 } // namespace blink
 
 #endif // LayoutBox_h