Issue 20827. Add imports as needed the 'Add type annotation' Quick Assist.

pkg/analysis_server/test/mock_sdk.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 testing.mock_sdk;
 
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
@@ skipping 71 matching lines @@
 
 void print(Object object) {}
 ''');
 
   static const _MockSdkLibrary LIB_ASYNC =
       const _MockSdkLibrary('dart:async', '/lib/async/async.dart', '''
 library dart.async;
 
 import 'dart:math';
 
-class Future {
+class Future<T> {
   static Future wait(List<Future> futures) => null;
 }
 
 class Stream<T> {}
 ''');
 
   static const _MockSdkLibrary LIB_MATH =
       const _MockSdkLibrary('dart:math', '/lib/math/math.dart', '''
 library dart.math;
 const double E = 2.718281828459045;
@@ skipping 150 matching lines @@
   bool get isInternal => throw unimplemented;
 
   @override
   bool get isShared => throw unimplemented;
 
   @override
   bool get isVmLibrary => throw unimplemented;
 
   UnimplementedError get unimplemented => new UnimplementedError();
 }