Update layout documentation re: coordinate systems and writing mode.

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

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h
index 5056ec97b002ea7b92fd4465db45dfc14781a35f..dbf9bd84b74acfb5630e3d3053d6baac67050544 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h
@@ -86,49 +86,8 @@ public:
 // design as it limits code sharing and prevents hardware accelerating SVG
 // (the current design require a PaintLayer for compositing).
 //
-//
-// ***** COORDINATE SYSTEMS *****
-//
-// In order to fully understand LayoutBoxModelObject and the inherited classes,
-// we need to introduce the concept of coordinate systems.
-// There is 3 main coordinate systems:
-// - physical coordinates: it is the coordinate system used for painting and
-//   correspond to physical direction as seen on the physical display (screen,
-//   printed page). In CSS, 'top', 'right', 'bottom', 'left' are all in physical
-//   coordinates. The code matches this convention too.
-//
-// - logical coordinates: this is the coordinate system used for layout. It is
-//   determined by 'writing-mode' and 'direction'. Any property using 'before',
-//   'after', 'start' or 'end' is in logical coordinates. Those are also named
-//   respectively 'logical top', 'logical bottom', 'logical left' and
-//   'logical right'.
-//
-// Example with writing-mode: vertical-rl; direction: ltr;
-//
-//                    'top' / 'start' side
-//
-//                     block-flow direction
-//           <------------------------------------ |
-//           ------------------------------------- |
-//           |        c   |          s           | |
-// 'left'    |        o   |          o           | |   inline     'right'
-//    /      |        n   |          m           | |  direction      /
-// 'after'   |        t   |          e           | |              'before'
-//  side     |        e   |                      | |                side
-//           |        n   |                      | |
-//           |        t   |                      | |
-//           ------------------------------------- v
-//
-//                 'bottom' / 'end' side
-//
-// See https://drafts.csswg.org/css-writing-modes-3/#text-flow for some
-// extra details.
-//
-// - physical coordinates with flipped block-flow direction: those are physical
-//   coordinates but we flipped the block direction. See
-//   LayoutBox::noOverflowRect.
-//   TODO(jchaffraix): I don't fully understand why we need this coordinate
-//   system someone should fill in those details.
+// For more on the coordinate systems used by this class and its subclasses, see
+// Source/core/layout/README.md ### Coordinate Spaces.

[eae, 2016/09/29 23:06:08]

Thank you for updating the README file, please leave a summary of the coordinate
system description in here (as a comment) though as everyone who looks at this
code will immediately see that. The overhead of looking at a raw markdown file
or finding a tool to translate it into HTML is much too high for it to replace a
well throughout inline description.

[wkorman, 2016/09/29 23:24:30]

Done.

 class CORE_EXPORT LayoutBoxModelObject : public LayoutObject {
 public:
     LayoutBoxModelObject(ContainerNode*);