Make _FileSystemWatcher.watch private.

sdk/lib/io/file_system_entity.dart

Index: sdk/lib/io/file_system_entity.dart
diff --git a/sdk/lib/io/file_system_entity.dart b/sdk/lib/io/file_system_entity.dart
index 5c15c1c8c87d99906fe76572e1474861de86d72f..f3923273adc63c205a3b4b254c2939b51b2a7e55 100644
--- a/sdk/lib/io/file_system_entity.dart
+++ b/sdk/lib/io/file_system_entity.dart
@@ -439,7 +439,7 @@ abstract class FileSystemEntity {
    */
   Stream<FileSystemEvent> watch({int events: FileSystemEvent.ALL,
                                  bool recursive: false})
-     => _FileSystemWatcher.watch(_trimTrailingPathSeparators(path),
+     => _FileSystemWatcher._watch(_trimTrailingPathSeparators(path),
                                  events,
                                  recursive);
 
@@ -827,7 +827,7 @@ class FileSystemMoveEvent extends FileSystemEvent {
 
 
 class _FileSystemWatcher {
-  external static Stream<FileSystemEvent> watch(
+  external static Stream<FileSystemEvent> _watch(
       String path, int events, bool recursive);
   external static bool get isSupported;
 }