Initial implementation of Collapsing Margins computational logic for LayoutNG

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 17a289eb3df05afdbe6782f08e2412372187b04a..c4be357477675a71fb3df86e2c90aa5bbcbbaf2f 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_units.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_units.h
@@ -9,6 +9,7 @@
 #include "core/layout/ng/ng_direction.h"
 #include "core/layout/ng/ng_writing_mode.h"
 #include "platform/LayoutUnit.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
@@ -116,6 +117,25 @@ struct NGBoxStrut {
   }
 };
 
+// This struct is used for the margin collapsing calculation.
+struct NGMarginStrut {
+  LayoutUnit margin_block_start;
+  LayoutUnit margin_block_end;
+
+  LayoutUnit negative_margin_block_start;
+  LayoutUnit negative_margin_block_end;
+
+  void AppendMarginBlockStart(const LayoutUnit& value);
+  void AppendMarginBlockEnd(const LayoutUnit& value);
+
+  String ToString() const;
+};
+
+inline std::ostream& operator<<(std::ostream& stream,
+                                const NGMarginStrut& value) {
+  return stream << value.ToString();
+}
+
 }  // namespace blink
 
 #endif  // NGUnits_h