Use different SDKs based on option settings

pkg/analysis_server/test/analysis/set_priority_files_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 test.analysis.set_priority_files;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show InternalAnalysisContext;
@@ skipping 40 matching lines @@
   }
 
   test_fileInSdk() async {
     addTestFile('');
     await server.onAnalysisComplete;
     // set priority files
     String filePath = '/lib/convert/convert.dart';
     Response response = await _setPriorityFile(filePath);
     expect(response, isResponseSuccess('0'));
     // verify
-    InternalAnalysisContext sdkContext = server.defaultSdk.context;
+    InternalAnalysisContext sdkContext = server.findSdk().context;
     List<Source> prioritySources = sdkContext.prioritySources;
     expect(prioritySources, hasLength(1));
     expect(prioritySources.first.fullName, filePath);
   }
 
   test_fileNotInAnalysisRoot() async {
     String path = '/other/file.dart';
     addFile(path, '');
     Response response = await _setPriorityFile(path);
     expect(response.error, isNotNull);
@@ skipping 51 matching lines @@
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.UNANALYZED_PRIORITY_FILES);
   }
 
   _setPriorityFile(String file) async {
     Request request =
         new AnalysisSetPriorityFilesParams(<String>[file]).toRequest('0');
     return await serverChannel.sendRequest(request);
   }
 }