Ignore zero-height fragments during margin collapsing

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 0ad2b1de44d7f423969c22430ce503ea2fd4d2c8..615132b38d3e9d83512eed927d29da067d82fbb2 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_units.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_units.h
@@ -110,6 +110,8 @@ struct NGBoxStrut {
   LayoutUnit InlineSum() const { return inline_start + inline_end; }
   LayoutUnit BlockSum() const { return block_start + block_end; }
 
+  bool IsEmpty() const;
+
   // The following two operators exist primarily to have an easy way to access
   // the sum of border and padding.
   NGBoxStrut& operator+=(const NGBoxStrut& other) {
@@ -125,6 +127,8 @@ struct NGBoxStrut {
     result += other;
     return result;
   }
+
+  bool operator==(const NGBoxStrut& other) const;
 };
 
 // This struct is used for the margin collapsing calculation.