Issue 24812. Fix for detached CompilationUnitElement(s) after package version switch.

pkg/analyzer/test/src/context/abstract_context.dart

 // Copyright (c) 2015, 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.src.task.abstract_context_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
@@ skipping 10 matching lines @@
 
 class AbstractContextTest {
   MemoryResourceProvider resourceProvider = new MemoryResourceProvider();
 
   DartSdk sdk = new MockSdk();
   SourceFactory sourceFactory;
   AnalysisContextImpl context;
   AnalysisCache analysisCache;
   AnalysisDriver analysisDriver;
 
+  UriResolver sdkResolver;
+  UriResolver resourceResolver;
+
   AnalysisTask task;
   Map<ResultDescriptor<dynamic>, dynamic> oldOutputs;
   Map<ResultDescriptor<dynamic>, dynamic> outputs;
 
   Source addSource(String path, String contents) {
     Source source = newSource(path, contents);
     ChangeSet changeSet = new ChangeSet();
     changeSet.addedSource(source);
     context.applyChanges(changeSet);
     return source;
@@ skipping 59 matching lines @@
   List<Source> newSources(Map<String, String> sourceMap) {
     List<Source> sources = <Source>[];
     sourceMap.forEach((String path, String content) {
       Source source = newSource(path, content);
       sources.add(source);
     });
     return sources;
   }
 
   void prepareAnalysisContext([AnalysisOptions options]) {
-    sourceFactory = new SourceFactory(<UriResolver>[
-      new DartUriResolver(sdk),
-      new ResourceUriResolver(resourceProvider)
-    ]);
+    sdkResolver = new DartUriResolver(sdk);
+    resourceResolver = new ResourceUriResolver(resourceProvider);
+    sourceFactory =
+        new SourceFactory(<UriResolver>[sdkResolver, resourceResolver]);
     context = createAnalysisContext();
     if (options != null) {
       context.analysisOptions = options;
     }
     context.sourceFactory = sourceFactory;
     analysisCache = context.analysisCache;
     analysisDriver = context.driver;
   }
 
   void setUp() {
     prepareAnalysisContext();
   }
 
   void tearDown() {}
 }