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

pkg/analysis_server/test/mocks.dart

Index: pkg/analysis_server/test/mocks.dart
diff --git a/pkg/analysis_server/test/mocks.dart b/pkg/analysis_server/test/mocks.dart
index c8b8078ccc431f9b3400795c841c096330133f90..7b898cbd4f53e7f059cc18d9ae99b47d009dd36c 100644
--- a/pkg/analysis_server/test/mocks.dart
+++ b/pkg/analysis_server/test/mocks.dart
@@ -5,7 +5,6 @@
 library mocks;
 
 import 'dart:async';
-import 'dart:convert';
 import 'dart:io';
 
 /**
@@ -13,10 +12,6 @@ import 'dart:io';
  */
 class MockSocket<T> implements WebSocket {
 
-  final JsonEncoder jsonEncoder = const JsonEncoder(null);
-
-  final JsonDecoder jsonDecoder = const JsonDecoder(null);
-
   StreamController controller = new StreamController();
   MockSocket twin;
   Stream stream;
@@ -50,4 +45,4 @@ class MockSocket<T> implements WebSocket {
   Stream<T> where(bool test(T)) => stream.where(test);
 
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
-}
+}