Don't depend on libdart_io in run_vm_tests and gen_snapshot.

runtime/bin/builtin_natives.cc

Index: runtime/bin/builtin_natives.cc
diff --git a/runtime/bin/builtin_natives.cc b/runtime/bin/builtin_natives.cc
index c5ef460dcfc7a0862f48acea42b161b81880fff4..f595a2c00890bda9af58e08cf627f4996068bec7 100644
--- a/runtime/bin/builtin_natives.cc
+++ b/runtime/bin/builtin_natives.cc
@@ -61,13 +61,6 @@ namespace bin {
   V(File_GetStdioHandleType, 1)                                                \
   V(File_GetType, 2)                                                           \
   V(File_AreIdentical, 2)                                                      \
-  V(FileSystemWatcher_CloseWatcher, 1)                                         \
-  V(FileSystemWatcher_GetSocketId, 2)                                          \
-  V(FileSystemWatcher_InitWatcher, 0)                                          \
-  V(FileSystemWatcher_IsSupported, 0)                                          \
-  V(FileSystemWatcher_ReadEvents, 2)                                           \
-  V(FileSystemWatcher_UnwatchPath, 2)                                          \
-  V(FileSystemWatcher_WatchPath, 4)                                            \
   V(Logger_PrintString, 1)
 
 BUILTIN_NATIVE_LIST(DECLARE_FUNCTION);