Really remove io support when dart:io is unsupported.

runtime/bin/file_system_watcher_unsupported.cc

Index: runtime/bin/file_system_watcher_unsupported.cc
diff --git a/runtime/bin/file_system_watcher_unsupported.cc b/runtime/bin/file_system_watcher_unsupported.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7803215bcadb0eb2846139a21590b7c9bd1d061a
--- /dev/null
+++ b/runtime/bin/file_system_watcher_unsupported.cc
@@ -0,0 +1,58 @@
+// Copyright (c) 2016, 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.
+
+#if defined(DART_IO_DISABLED)
+
+#include "bin/builtin.h"
+#include "bin/dartutils.h"
+#include "include/dart_api.h"
+
+namespace dart {
+namespace bin {
+
+void FUNCTION_NAME(FileSystemWatcher_IsSupported)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_InitWatcher)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_CloseWatcher)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_WatchPath)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_UnwatchPath)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_ReadEvents)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+
+void FUNCTION_NAME(FileSystemWatcher_GetSocketId)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewInternalError(
+        "FileSystemWatcher is not supported on this platform"));
+}
+
+}  // namespace bin
+}  // namespace dart
+
+#endif  // defined(DART_IO_DISABLED)