Add implicit dart:core import when resynthsize from Kernel.

pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart

Index: pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart b/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
index cc085ff2355abe9252bb507a1e768a3038245ae7..6c2b84e7a6a78782b866ff53886d312fe0402afe 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
@@ -14,11 +14,11 @@ import 'package:analyzer/src/kernel/resynthesize.dart';
 import 'package:analyzer/src/summary/resynthesize.dart';
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/file_system.dart';
-import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/base/libraries_specification.dart';
+import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/base/processed_options.dart';
-import 'package:front_end/src/fasta/uri_translator_impl.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
+import 'package:front_end/src/fasta/uri_translator_impl.dart';
 import 'package:front_end/src/incremental/kernel_driver.dart';
 import 'package:kernel/kernel.dart' as kernel;
 import 'package:kernel/target/targets.dart';
@@ -500,11 +500,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
     await super.test_import_invalidUri_metadata();
   }
 
-  @failingTest
-  test_import_self() async {
-    await super.test_import_self();
-  }
-
   @failingTest
   test_inferred_type_refers_to_function_typed_param_of_typedef() async {
     await super.test_inferred_type_refers_to_function_typed_param_of_typedef();