Add FileSystemWatcher class to dart:io.

runtime/bin/builtin_natives.cc

 // Copyright (c) 2012, 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.
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 
 #include "include/dart_api.h"
 
@@ skipping 42 matching lines @@
   V(File_Delete, 1)                                                            \
   V(File_DeleteLink, 1)                                                        \
   V(File_Rename, 2)                                                            \
   V(File_RenameLink, 2)                                                        \
   V(File_FullPath, 1)                                                          \
   V(File_OpenStdio, 1)                                                         \
   V(File_GetStdioHandleType, 1)                                                \
   V(File_GetType, 2)                                                           \
   V(File_AreIdentical, 2)                                                      \
   V(File_NewServicePort, 0)                                                    \
+  V(FileSystemWatcher_ReadEvents, 1)                                           \
+  V(FileSystemWatcher_UnwatchPath, 1)                                          \
+  V(FileSystemWatcher_WatchPath, 4)                                            \
   V(Logger_PrintString, 1)
 
 BUILTIN_NATIVE_LIST(DECLARE_FUNCTION);
 
 static struct NativeEntries {
   const char* name_;
   Dart_NativeFunction function_;
   int argument_count_;
 } BuiltinEntries[] = {
   BUILTIN_NATIVE_LIST(REGISTER_FUNCTION)
@@ skipping 36 matching lines @@
     fputs(Dart_GetError(result), stdout);
   } else {
     fwrite(chars, sizeof(*chars), length, stdout);
   }
   fputc('\n', stdout);
   fflush(stdout);
 }
 
 }  // namespace bin
 }  // namespace dart