Reland "Let SVGForeignObject's local SVG coordinates mean what it should"

third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef LayoutSVGBlock_h
 #define LayoutSVGBlock_h
 
 #include "core/layout/LayoutBlockFlow.h"
 
 namespace blink {
 
 class SVGElement;
 
+// A common class of SVG objects that delegate layout, paint, etc. tasks to
+// LayoutBlockFlow. It has two coordinate spaces:
+// - local SVG coordinate space: similar to LayoutSVGModelObject, the space
+//   that localSVGTransform() applies.
+// - local HTML coordinate space: defined by frameRect() as if the local SVG
+//   coordinate space created a containing block. Like other LayoutBlockFlow
+//   objects, LayoutSVGBlock's frameRect() is also in physical coordinates with
+//   flipped blocks direction in the "containing block".
 class LayoutSVGBlock : public LayoutBlockFlow {
  public:
   explicit LayoutSVGBlock(SVGElement*);
 
+  // These mapping functions map coordinates in HTML spaces.
   void mapLocalToAncestor(const LayoutBoxModelObject* ancestor,
                           TransformState&,
                           MapCoordinatesFlags = ApplyContainerFlip) const final;
   void mapAncestorToLocal(const LayoutBoxModelObject* ancestor,
                           TransformState&,
                           MapCoordinatesFlags = ApplyContainerFlip) const final;
   const LayoutObject* pushMappingToContainer(
       const LayoutBoxModelObject* ancestorToStopAt,
       LayoutGeometryMap&) const final;
 
@@ skipping 31 matching lines @@
                    HitTestAction) override;
 
   // The inherited version doesn't check for SVG effects.
   bool paintedOutputOfObjectHasNoEffectRegardlessOfSize() const override {
     return false;
   }
 };
 
 }  // namespace blink
 #endif  // LayoutSVGBlock_h