Don't depend on libdart_io in run_vm_tests and gen_snapshot.

runtime/bin/io_natives.cc

Index: runtime/bin/io_natives.cc
diff --git a/runtime/bin/io_natives.cc b/runtime/bin/io_natives.cc
index 6a860b7d66da24c8c07e46dfa5f55f5c67972a58..90a6263c4cfe6a3f0055660165070ed8f0914b65 100644
--- a/runtime/bin/io_natives.cc
+++ b/runtime/bin/io_natives.cc
@@ -22,6 +22,13 @@ namespace bin {
 #define IO_NATIVE_LIST(V)                                                      \
   V(Crypto_GetRandomBytes, 1)                                                  \
   V(EventHandler_SendData, 3)                                                  \
+  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(Filter_CreateZLibDeflate, 3)                                               \
   V(Filter_CreateZLibInflate, 1)                                               \
   V(Filter_End, 1)                                                             \