add file watching support

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 165 matching lines @@
 
 /**
  * An in-memory implementation of [File] which acts like a symbolic link to a
  * non-existent file.
  */
 class _MemoryDummyLink extends _MemoryResource implements File {
   _MemoryDummyLink(MemoryResourceProvider provider, String path)
       : super(provider, path);
 
   @override
+  Stream<WatchEvent> get changes {
+    throw new FileSystemException(path, "File does not exist");
+  }
+
+  @override
   bool get exists => false;
 
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];
     if (stamp == null) {
       throw new FileSystemException(path, "File does not exist");
     }
     return stamp;
   }
 
@@ skipping 155 matching lines @@
 }
 
 /**
  * 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;
   }
 
@@ skipping 47 matching lines @@
 
 /**
  * An in-memory implementation of [Resource].
  */
 abstract class _MemoryResource implements Resource {
   final MemoryResourceProvider _provider;
   final String path;
 
   _MemoryResource(this._provider, this.path);
 
+  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
   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;
 }