fix list_test for strong mode, and fix DDC List constructors

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
index 91f541ea3cf5789bb0091a2c03ac2ee745ba91be..13d0a3ad42d88ff38422430377d02bb3db3d343f 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
@@ -858,9 +858,9 @@ constList(elements, elementType) => JS('', '''(() => {
   let value = map.get($elementType);
   if (value) return value;
 
-  value = $setType($elements, ${getGenericClass(JSArray)}($elementType));
-  map.set($elementType, value);
-  return value;
+  ${getGenericClass(JSArray)}($elementType).unmodifiable($elements);
+  map.set($elementType, elements);
+  return elements;
 })()''');
 
 // The following are helpers for Object methods when the receiver