[LayoutNG] Don't implement ContainerSize() using the physical constraint space.

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 4662a766d9c3fd4c3f1c3c01cc7d221e28c27453..9a69af13a7ad00cb90fb90433d5a4b4488bbf09d 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
@@ -65,7 +65,7 @@ class CORE_EXPORT NGConstraintSpace final
   // 3) Defining the threshold that triggers the presence of a scrollbar. Only
   //    applies if the corresponding scrollbarTrigger flag has been set for the
   //    direction.
-  NGLogicalSize ContainerSize() const;
+  NGLogicalSize ContainerSize() const { return size_; }
 
   // Offset relative to the root constraint space.
   NGLogicalOffset Offset() const { return offset_; }