Add FunctionType.getNamedParameter.

pkg/kernel/lib/type_checker.dart

Index: pkg/kernel/lib/type_checker.dart
diff --git a/pkg/kernel/lib/type_checker.dart b/pkg/kernel/lib/type_checker.dart
index 6c48a6d91d17175c928b6e0c574200e659ab3fb9..f32ae870cdd3f9a133f171d228c6e5397633e9c4 100644
--- a/pkg/kernel/lib/type_checker.dart
+++ b/pkg/kernel/lib/type_checker.dart
@@ -497,19 +497,13 @@ class TypeCheckingVisitor
     }
     for (int i = 0; i < arguments.named.length; ++i) {
       var argument = arguments.named[i];
-      bool found = false;
-      for (int j = 0; j < function.namedParameters.length; ++j) {
-        if (argument.name == function.namedParameters[j].name) {
-          var expectedType = instantiation.substituteType(
-              function.namedParameters[j].type,
-              contravariant: true);
-          argument.value =
-              checkAndDowncastExpression(argument.value, expectedType);
-          found = true;
-          break;
-        }
-      }
-      if (!found) {
+      var parameterType = function.getNamedParameter(argument.name);
+      if (parameterType != null) {
+        var expectedType =
+            instantiation.substituteType(parameterType, contravariant: true);
+        argument.value =
+            checkAndDowncastExpression(argument.value, expectedType);
+      } else {
         fail(argument.value, 'Unexpected named parameter: ${argument.name}');
         return const BottomType();
       }