Preserve type variables in closure conversion.

pkg/kernel/lib/ast.dart

Index: pkg/kernel/lib/ast.dart
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 5c432803f549d673c68e4be3251a29179143b1d6..722da644f18587a22a89b504c2a7f050dc05a170 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -3076,14 +3076,15 @@ class ClosureCreation extends Expression {
   Reference topLevelFunctionReference;
   Expression contextVector;
   FunctionType functionType;
+  List<DartType> typeArguments;
 
   ClosureCreation(Member topLevelFunction, Expression contextVector,
-      FunctionType functionType)
-      : this.byReference(
-            getMemberReference(topLevelFunction), contextVector, functionType);
+      FunctionType functionType, List<DartType> typeArguments)
+      : this.byReference(getMemberReference(topLevelFunction), contextVector,
+            functionType, typeArguments);
 
-  ClosureCreation.byReference(
-      this.topLevelFunctionReference, this.contextVector, this.functionType) {
+  ClosureCreation.byReference(this.topLevelFunctionReference,
+      this.contextVector, this.functionType, this.typeArguments) {
     contextVector?.parent = this;
   }
 
@@ -3098,6 +3099,8 @@ class ClosureCreation extends Expression {
 
   visitChildren(Visitor v) {
     contextVector?.accept(v);
+    functionType.accept(v);
+    visitList(typeArguments, v);
   }
 
   transformChildren(Transformer v) {
@@ -3105,6 +3108,8 @@ class ClosureCreation extends Expression {
       contextVector = contextVector.accept(v);
       contextVector?.parent = this;
     }
+    functionType = v.visitDartType(functionType);
+    transformTypeList(typeArguments, v);
   }
 
   DartType getStaticType(TypeEnvironment types) {