gracefully degrade with response to client if fail to access client specified dart sdk

pkg/analysis_server/test/protocol_test.dart

Index: pkg/analysis_server/test/protocol_test.dart
diff --git a/pkg/analysis_server/test/protocol_test.dart b/pkg/analysis_server/test/protocol_test.dart
index 2767cc72d1dd51bddac8332c53f0186e5304425e..ae5eac922be4c783609fbbcc7cee42d0059a4605 100644
--- a/pkg/analysis_server/test/protocol_test.dart
+++ b/pkg/analysis_server/test/protocol_test.dart
@@ -113,7 +113,7 @@ class RequestTest {
 
   static void fromJson() {
     Request original = new Request('one', 'aMethod');
-    String json = new JsonEncoder(null).convert(original.toJson());
+    String json = JSON.encode(original.toJson());
     Request request = new Request.fromString(json);
     expect(request.id, equals('one'));
     expect(request.method, equals('aMethod'));
@@ -140,7 +140,7 @@ class RequestTest {
   static void fromJson_withParams() {
     Request original = new Request('one', 'aMethod');
     original.setParameter('foo', 'bar');
-    String json = new JsonEncoder(null).convert(original.toJson());
+    String json = JSON.encode(original.toJson());
     Request request = new Request.fromString(json);
     expect(request.id, equals('one'));
     expect(request.method, equals('aMethod'));