Implement collection of out-of-flow descendants

third_party/WebKit/Source/core/layout/ng/ng_units.h

Index: third_party/WebKit/Source/core/layout/ng/ng_units.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_units.h b/third_party/WebKit/Source/core/layout/ng/ng_units.h
index 95151cc9e863cfc917fade2a82b04378dd7993f2..5eb36a25c9d7e1cfe5bc219e988061291dfe57c0 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_units.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_units.h
@@ -57,6 +57,9 @@ struct NGLogicalOffset {
 
   // Converts a logical offset to a physical offset. See:
   // https://drafts.csswg.org/css-writing-modes-3/#logical-to-physical
+  // PhysicalOffset will be the physical top left point of the rectangle
+  // described by offset + inner_size. Setting inner_size to 0,0 will return
+  // the same point.
   // @param outer_size the size of the rect (typically a fragment).
   // @param inner_size the size of the inner rect (typically a child fragment).
   CORE_EXPORT NGPhysicalOffset
@@ -64,6 +67,7 @@ struct NGLogicalOffset {
                     TextDirection,
                     NGPhysicalSize outer_size,
                     NGPhysicalSize inner_size) const;
+
   bool operator==(const NGLogicalOffset& other) const;
 
   NGLogicalOffset operator+(const NGLogicalOffset& other) const;
@@ -92,6 +96,9 @@ struct NGPhysicalOffset {
 
   LayoutUnit left;
   LayoutUnit top;
+
+  NGPhysicalOffset operator+(const NGPhysicalOffset& other) const;
+  NGPhysicalOffset& operator+=(const NGPhysicalOffset& other);
 };
 
 struct NGPhysicalSize {
@@ -267,6 +274,17 @@ struct NGEdge {
   LayoutUnit end;
 };
 
+// Represents static position of an out of flow descendant.
+struct CORE_EXPORT NGCorner {

[ikilpatrick, 2016/12/02 21:06:13]

I half wonder if this should be named NGStaticPosition, but can think about it
later.
(no action required).

+  enum Type { kTopLeft, kTopRight, kBottomLeft, kBottomRight };
+
+  Type type;  // Logical corner that corresponds to physical top left.
+  NGPhysicalOffset offset;
+
+  // Creates a corner with proper type wrt writing mode and direction.
+  static NGCorner Create(NGWritingMode, TextDirection, NGPhysicalOffset);
+};
+
 }  // namespace blink
 
 #endif  // NGUnits_h