ContextBuilder should to throw when a root folder does not exist.

pkg/analysis_server/test/context_manager_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.context.directory.manager;
 
 import 'dart:collection';
 
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/utilities/null_string_sink.dart';
@@ skipping 2070 matching lines @@
         [projPath, optionsFileName],
         r'''
 ;
 ''');
     // Setup context.
     manager.setRoots(<String>[projPath], <String>[], <String, String>{});
 
     // No error means success.
   }
 
+  test_deleteRoot_hasAnalysisOptions() async {
+    newFile([projPath, optionsFileName], '');
+
+    // Add the root.
+    manager.setRoots(<String>[projPath], <String>[], <String, String>{});
+    await pumpEventQueue();
+
+    // Remove the root, with the analysis options file.
+    // No exceptions.
+    resourceProvider.deleteFolder(projPath);
+    await pumpEventQueue();
+  }
+
   test_embedder_options() async {
     // Create files.
     String libPath = newFolder([projPath, ContextManagerTest.LIB_NAME]);
     String sdkExtPath = newFolder([projPath, 'sdk_ext']);
     newFile([projPath, 'test', 'test.dart']);
     newFile([sdkExtPath, 'entry.dart']);
     List<int> bytes = new SummaryBuilder([], null, true).build();
     newFileFromBytes([projPath, 'sdk.ds'], bytes);
     // Setup _embedder.yaml.
     newFile(
@@ skipping 783 matching lines @@
 class TestUriResolver extends UriResolver {
   Map<Uri, Source> uriMap;
 
   TestUriResolver(this.uriMap);
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     return uriMap[uri];
   }
 }