Fix for the watcher leak.

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 386 matching lines @@
   /**
    * Virtual [ContextInfo] which acts as the ancestor of all other
    * [ContextInfo]s.
    */
   final ContextInfo _rootInfo = new ContextInfo._root();
 
   /**
    * Stream subscription we are using to watch each analysis root directory for
    * changes.
    */
-  final Map<Folder, StreamSubscription<WatchEvent>> _changeSubscriptions =
+  final Map<Folder, StreamSubscription<WatchEvent>> changeSubscriptions =
       <Folder, StreamSubscription<WatchEvent>>{};
 
   ContextManagerImpl(this.resourceProvider, this.packageResolverProvider,
       this._packageMapProvider, this._instrumentationService) {
     pathContext = resourceProvider.pathContext;
   }
 
   @override
   List<AnalysisContext> contextsInAnalysisRoot(Folder analysisRoot) {
     List<AnalysisContext> contexts = <AnalysisContext>[];
@@ skipping 176 matching lines @@
         info.packageRoot = newPackageRoot;
         _recomputeFolderDisposition(info);
       }
     }
     // create new contexts
     for (Folder includedFolder in includedFolders) {
       bool wasIncluded = contextInfos.any((info) {
         return info.folder.isOrContains(includedFolder.path);
       });
       if (!wasIncluded) {
-        _changeSubscriptions[includedFolder] =
+        changeSubscriptions[includedFolder] =
             includedFolder.changes.listen(_handleWatchEvent);
         _createContexts(_rootInfo, includedFolder, false);
       }
     }
     // remove newly excluded sources
     for (ContextInfo info in _rootInfo.descendants) {
       // prepare excluded sources
       Map<String, Source> excludedSources = new HashMap<String, Source>();
       info.sources.forEach((String path, Source source) {
         if (_isExcludedBy(excludedPaths, path) &&
@@ skipping 313 matching lines @@
       ChangeSet changeSet = new ChangeSet();
       _addSourceFiles(changeSet, folder, parent);
       callbacks.applyChangesToContext(folder, changeSet);
     }
   }
 
   /**
    * Clean up and destroy the context associated with the given folder.
    */
   void _destroyContext(ContextInfo info) {
-    if (_changeSubscriptions.containsKey(info.folder)) {
-      _changeSubscriptions[info.folder].cancel();
-    }
+    changeSubscriptions.remove(info.folder)?.cancel();
     callbacks.removeContext(info.folder, _computeFlushedFiles(info));
     bool wasRemoved = info.parent.children.remove(info);
     assert(wasRemoved);
   }
 
   /**
    * Extract a new [packagespecFile]-based context from [oldInfo].
    */
   void _extractContext(ContextInfo oldInfo, File packagespecFile) {
     Folder newFolder = packagespecFile.parent;
@@ skipping 496 matching lines @@
           var path = resourceProvider.pathContext.fromUri(uri);
           packageMap[name] = <Folder>[resourceProvider.getFolder(path)];
         }
       });
       return <UriResolver>[new SdkExtUriResolver(packageMap)];
     } else {
       return const <UriResolver>[];
     }
   }
 }