Really remove io support when dart:io is unsupported.

runtime/bin/eventhandler_android.cc

Index: runtime/bin/eventhandler_android.cc
diff --git a/runtime/bin/eventhandler_android.cc b/runtime/bin/eventhandler_android.cc
index 5daeb78df0f1d378dc2650df8889ef14a1911f9f..1b7bbdb0c53b4192aa2afa2edbbfcb20b41eeac0 100644
--- a/runtime/bin/eventhandler_android.cc
+++ b/runtime/bin/eventhandler_android.cc
@@ -2,6 +2,8 @@
 // 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 "platform/globals.h"
 #if defined(TARGET_OS_ANDROID)
 
@@ -433,3 +435,5 @@ uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_ANDROID)
+
+#endif  // !defined(DART_IO_DISABLED)