Use shared MockSdk instances in resynthesize tests.

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

Index: pkg/analyzer/test/src/summary/resynthesize_strong_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_strong_test.dart b/pkg/analyzer/test/src/summary/resynthesize_strong_test.dart
index 6520f5383b283244f83811a4cefeacc09d3cfb96..c52b60482f1e91ff2330cd5c696871a213d13cff 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_strong_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_strong_test.dart
@@ -5,9 +5,11 @@
 library analyzer.test.src.summary.resynthesize_strong_test;
 
 import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/sdk.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
+import '../context/abstract_context.dart';
 import 'resynthesize_test.dart';
 
 main() {
@@ -17,6 +19,8 @@ main() {
 
 @reflectiveTest
 class ResynthesizeStrongTest extends ResynthesizeElementTest {
+  DartSdk createDartSdk() => AbstractContextTest.SHARED_STRONG_MOCK_SDK;
+
   @override
   AnalysisOptionsImpl createOptions() =>
       super.createOptions()..strongMode = true;