[kernel] Fix legacy types appearing when sound

Calling these apis would return a legacy type even when
compiling a program for sound null safety.

Change-Id: Ia7f177ac7da09ddff865a4a935d06c4830f6da07
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/327903
Commit-Queue: Nicholas Shahan <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: nshahan

pkg/front_end/test/fasta/types/dill_hierarchy_test.dart

@@ -40,37 +40,37 @@ Object:
 
 A:
   superclasses:
-    Object
+    Object!
 
 B:
   Longest path to Object: 2
   superclasses:
-    Object
-  interfaces: A
+    Object!
+  interfaces: A!
 
 C:
   Longest path to Object: 2
   superclasses:
-    Object
-  interfaces: A
+    Object!
+  interfaces: A!
 
 D:
   Longest path to Object: 3
   superclasses:
-    Object
-  interfaces: B<T%>, A, C<U%>
+    Object!
+  interfaces: B<T%>!, A!, C<U%>!
 
 E:
   Longest path to Object: 4
   superclasses:
-    Object
-  interfaces: D<int!,double!>, B<int!>, A, C<double!>
+    Object!
+  interfaces: D<int!,double!>!, B<int!>!, A!, C<double!>!
 
 F:
   Longest path to Object: 4
   superclasses:
-    Object
-  interfaces: D<int!,bool!>, B<int!>, A, C<bool!>
+    Object!
+  interfaces: D<int!,bool!>!, B<int!>!, A!, C<bool!>!
 """;
 
 void main() {

pkg/kernel/lib/ast.dart

@@ -6597,10 +6597,10 @@ class ConstructorInvocation extends InvocationExpression {
     // TODO(cstefantsova): Get raw type from a CoreTypes object if arguments is
     // empty.
     return arguments.types.isEmpty
-        ? new InterfaceType(
-            enclosingClass, Nullability.legacy, const <DartType>[])
-        : new InterfaceType(
-            enclosingClass, Nullability.legacy, arguments.types);
+        ? new InterfaceType(enclosingClass, target.enclosingLibrary.nonNullable,
+            const <DartType>[])
+        : new InterfaceType(enclosingClass, target.enclosingLibrary.nonNullable,
+            arguments.types);
   }
 
   @override
@@ -13123,7 +13123,8 @@ class Supertype extends Node {
   }
 
   InterfaceType get asInterfaceType {
-    return new InterfaceType(classNode, Nullability.legacy, typeArguments);
+    return new InterfaceType(
+        classNode, classNode.enclosingLibrary.nonNullable, typeArguments);
   }
 
   @override