Ignore non-existent analysis roots.

pkg/analysis_server/lib/src/context_manager.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 context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:core' hide Resource;
@@ skipping 513 matching lines @@
     });
 
     List<ContextInfo> contextInfos = _rootInfo.descendants.toList();
     // included
     Set<Folder> includedFolders = new HashSet<Folder>();
     for (int i = 0; i < includedPaths.length; i++) {
       String path = includedPaths[i];
       Resource resource = resourceProvider.getResource(path);
       if (resource is Folder) {
         includedFolders.add(resource);
+      } else if (!resource.exists) {
+        // Non-existent resources are ignored.  TODO(paulberry): we should set
+        // up a watcher to ensure that if the resource appears later, we will
+        // begin analyzing it.
       } else {
         // TODO(scheglov) implemented separate files analysis
         throw new UnimplementedError('$path is not a folder. '
             'Only support for folder analysis is implemented currently.');
       }
     }
     this.includedPaths = includedPaths;
     // excluded
     List<String> oldExcludedPaths = this.excludedPaths;
     this.excludedPaths = excludedPaths;
@@ skipping 837 matching lines @@
           var path = resourceProvider.pathContext.fromUri(uri);
           packageMap[name] = <Folder>[resourceProvider.getFolder(path)];
         }
       });
       return <UriResolver>[new SdkExtUriResolver(packageMap)];
     } else {
       return const <UriResolver>[];
     }
   }
 }