Make _LinuxDirectoryWatcher._listen generic (dart-lang/watcher#45)

pkgs/watcher/lib/src/directory_watcher/linux.dart

diff --git a/pkgs/watcher/lib/src/directory_watcher/linux.dart b/pkgs/watcher/lib/src/directory_watcher/linux.dart
index 717e420..354ddc0 100644
--- a/pkgs/watcher/lib/src/directory_watcher/linux.dart
+++ b/pkgs/watcher/lib/src/directory_watcher/linux.dart
@@ -127,8 +127,7 @@
   }
 
   /// The callback that's run when a batch of changes comes in.
-  void _onBatch(Object data) {
-    var batch = data as List<FileSystemEvent>;
+  void _onBatch(List<FileSystemEvent> batch) {
     var files = new Set<String>();
     var dirs = new Set<String>();
     var changed = new Set<String>();
@@ -251,7 +250,7 @@
 
   /// Like [Stream.listen], but automatically adds the subscription to
   /// [_subscriptions] so that it can be canceled when [close] is called.
-  void _listen(Stream stream, void onData(event),
+  void _listen<T>(Stream<T> stream, void onData(T event),
       {Function onError, void onDone(), bool cancelOnError}) {
     var subscription;
     subscription = stream.listen(onData, onError: onError, onDone: () {