Don't do folder existence checks when parsing pub list results.

pkg/analyzer/lib/file_system/memory_file_system.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 memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
@@ skipping 156 matching lines @@
 }
 
 
 /**
  * An in-memory implementation of [File].
  */
 class _MemoryFile extends _MemoryResource implements File {
   _MemoryFile(MemoryResourceProvider provider, String path)
       : super(provider, path);
 
+  @override
+  bool get exists => _provider._pathToResource[path] is _MemoryFile;
+
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];
     if (stamp == null) {
       throw new FileSystemException(path, 'File does not exist.');
     }
     return stamp;
   }
 
   String get _content {
     String content = _provider._pathToContent[path];
@@ skipping 92 matching lines @@
   String toString() => _file.toString();
 }
 
 
 /**
  * An in-memory implementation of [Folder].
  */
 class _MemoryFolder extends _MemoryResource implements Folder {
   _MemoryFolder(MemoryResourceProvider provider, String path)
       : super(provider, path);
+
   @override
   Stream<WatchEvent> get changes {
     StreamController<WatchEvent> streamController =
         new StreamController<WatchEvent>();
     if (!_provider._pathToWatchers.containsKey(path)) {
       _provider._pathToWatchers[path] = <StreamController<WatchEvent>>[];
     }
     _provider._pathToWatchers[path].add(streamController);
     streamController.done.then((_) {
       _provider._pathToWatchers[path].remove(streamController);
       if (_provider._pathToWatchers[path].isEmpty) {
         _provider._pathToWatchers.remove(path);
       }
     });
     return streamController.stream;
   }
 
   @override
+  bool get exists => _provider._pathToResource[path] is _MemoryFolder;
+
+  @override
   String canonicalizePath(String relPath) {
     relPath = posix.normalize(relPath);
     String childPath = posix.join(path, relPath);
     childPath = posix.normalize(childPath);
     return childPath;
   }
 
   @override
   bool contains(String path) {
     return posix.isWithin(this.path, path);
   }
 
   @override
   Resource getChild(String relPath) {
     String childPath = canonicalizePath(relPath);
     _MemoryResource resource = _provider._pathToResource[childPath];
     if (resource == null) {
       resource = new _MemoryFile(_provider, childPath);
     }
     return resource;
   }
 
   @override
+  _MemoryFolder getChildAssumingFolder(String relPath) {
+    String childPath = canonicalizePath(relPath);
+    _MemoryResource resource = _provider._pathToResource[childPath];
+    if (resource is _MemoryFolder) {
+      return resource;
+    }
+    return new _MemoryFolder(_provider, childPath);
+  }
+
+  @override
   List<Resource> getChildren() {
     List<Resource> children = <Resource>[];
     _provider._pathToResource.forEach((resourcePath, resource) {
       if (posix.dirname(resourcePath) == path) {
         children.add(resource);
       }
     });
     return children;
   }
 
@@ skipping 10 matching lines @@
 /**
  * An in-memory implementation of [Resource].
  */
 abstract class _MemoryResource implements Resource {
   final MemoryResourceProvider _provider;
   final String path;
 
   _MemoryResource(this._provider, this.path);
 
   @override
-  bool get exists => _provider._pathToResource.containsKey(path);
-
-  @override
   get hashCode => path.hashCode;
 
   @override
   Folder get parent {
     String parentPath = posix.dirname(path);
     if (parentPath == path) {
       return null;
     }
     return _provider.getResource(parentPath);
   }
 
   @override
   String get shortName => posix.basename(path);
 
   @override
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }