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

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

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h b/third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h
index 925c4871e2a38703dd25032bfe5123863395ae58..3160899c9e18df8fd239725fb587812dd5e51fba 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGBlock.h
@@ -26,10 +26,19 @@ 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;