Update mock compiler.

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2012, 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 mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:collection';
 import 'dart:uri';
 
@@ skipping 41 matching lines @@
   boolConversionCheck(x) {}
   abstract class JavaScriptIndexingBehavior {}
   class JSInvocationMirror {}
   class Closure {}
   class Null {}
   class Dynamic_ {}
   class LinkedHashMap {}
   class ConstantMap {}
   class TypeImpl {}
   S() {}
+  throwExpression(e) {}
   unwrapException(e) {}
   assertHelper(a){}
   createRuntimeType(a) {}
   createInvocationMirror(a0, a1, a2, a3, a4, a5) {}
   throwNoSuchMethod(obj, name, arguments, expectedArgumentNames) {}
   throwAbstractClassInstantiationError(className) {}''';
 
 const String FOREIGN_LIBRARY = r'''
   dynamic JS(String typeDescription, String codeTemplate,
     [var arg0, var arg1, var arg2, var arg3, var arg4, var arg5, var arg6,
@@ skipping 327 matching lines @@
   }
 }
 
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   void registerMainApp(LibraryElement mainApp) {
     // Do nothing.
   }
 }