[layoutng] Create a more correct constraint space for children

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

Index: third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
index 28be146e47020bdb6be8d2414b55ece8ba5744df..b924de5ec726019fafa50cc4264d040cc6770910 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
@@ -53,6 +53,10 @@ class CORE_EXPORT NGConstraintSpace {
   NGConstraintSpace(NGLogicalSize container_size);
   virtual ~NGConstraintSpace() {}
 
+  // Constructs a new constraint space based on an old one with a new size but
+  // the same exclusions.
+  NGConstraintSpace(const NGConstraintSpace&, NGLogicalSize container_size);
+
   // Constructs Layout NG constraint space from legacy layout object.
   static NGConstraintSpace fromLayoutObject(const LayoutBox&);