Fix patch file return types

sdk/lib/_internal/compiler/implementation/lib/io_patch.dart

Index: sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart b/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
index 098e893cb70a31cee7a37e9e83fc46ddd65a0e72..9b38456697fd36b92e032d7267180fa1992c847b 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
@@ -162,16 +162,16 @@ patch class _Platform {
 }
 
 patch class _ProcessUtils {
-  patch static _exit(int status) {
+  patch static void _exit(int status) {
     throw new UnsupportedError("ProcessUtils._exit");
   }
-  patch static _setExitCode(int status) {
+  patch static void _setExitCode(int status) {
     throw new UnsupportedError("ProcessUtils._setExitCode");
   }
-  patch static _sleep(int millis) {
+  patch static void _sleep(int millis) {
     throw new UnsupportedError("ProcessUtils._sleep");
   }
-  patch static _pid(Process process) {
+  patch static int _pid(Process process) {
     throw new UnsupportedError("ProcessUtils._pid");
   }
 }