Update MockSdk to be more consistent with the actual SDK, switch x_Driver tests to it.

pkg/analyzer/test/generated/compile_time_error_code_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.generated.compile_time_error_code_test;
 
 import 'dart:async';
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/error/codes.dart';
@@ skipping 2755 matching lines @@
     // we could prevent the hint from being generated by testing the import
     // directive for the error, this is such a minor corner case that we don't
     // think we should add the additional computation time to figure out such
     // cases.
     await computeAnalysisResult(source);
     assertErrors(source,
         [CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY, HintCode.UNUSED_IMPORT]);
     verify([source]);
   }
 
-  test_importInternalLibrary_js_helper() async {
-    Source source = addSource("import 'dart:_js_helper';");
-    // Note, in these error cases we may generate an UNUSED_IMPORT hint, while
-    // we could prevent the hint from being generated by testing the import
-    // directive for the error, this is such a minor corner case that we don't
-    // think we should add the additional computation time to figure out such
-    // cases.
-    await computeAnalysisResult(source);
-    assertErrors(source,
-        [CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY, HintCode.UNUSED_IMPORT]);
-    verify([source]);
-  }
-
   test_importOfNonLibrary() async {
     Source source = addSource(r'''
 library lib;
 import 'part.dart';
 A a;''');
     addNamedSource(
         "/part.dart",
         r'''
 part of lib;
 class A{}''');
@@ skipping 3658 matching lines @@
         source, [CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR]);
     verify([source]);
     reset();
   }
 
   Future<Null> _check_wrongNumberOfParametersForOperator1(String name) async {
     await _check_wrongNumberOfParametersForOperator(name, "");
     await _check_wrongNumberOfParametersForOperator(name, "a, b");
   }
 }