Simplify how patch files are specified to analyzer.

pkg/analyzer/test/src/context/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 analyzer.test.src.context.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/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
@@ skipping 503 matching lines @@
   bool get isImplementation => throw new UnimplementedError();
 
   @override
   bool get isInternal => throw new UnimplementedError();
 
   @override
   bool get isShared => throw new UnimplementedError();
 
   @override
   bool get isVmLibrary => throw new UnimplementedError();
-
-  @override
-  List<String> getPatches(int platform) => const <String>[];
 }
 
 /**
  * An [AnalysisContextImpl] that only contains sources for a Dart SDK.
  */
 class _SdkAnalysisContext extends AnalysisContextImpl {
   final DartSdk sdk;
 
   _SdkAnalysisContext(this.sdk);
 
   @override
   AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
     if (factory == null) {
       return super.createCacheFromSourceFactory(factory);
     }
     return new AnalysisCache(
         <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }