Resynthesize ?? expressions 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 0106280f6e4a24d89a844c1af8d2a6fde8482e56..b75832f8365e39082775cabea47456bc76620261 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
@@ -113,6 +113,7 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
   }
 
   @failingTest
+  @fastaProblem
   test_class_constructor_field_formal_multiple_matching_fields() async {
     // Fasta does not generate the class.
     // main() with a fatal error is generated instead.
@@ -236,11 +237,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
     await super.test_const_reference_unresolved_prefix2();
   }
 
-  @failingTest
-  test_const_topLevel_ifNull() async {
-    await super.test_const_topLevel_ifNull();
-  }
-
   @failingTest
   @fastaProblem
   test_const_topLevel_super() async {