Fix pub to work with new Directory.createSystemTemp.

sdk/lib/_internal/pub/test/test_pub.dart

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index 1f79116a6b243943a247facf7d468e6de1bffee0..fc449c2953f459b093f8731f47b57f0668fb9d62 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -337,7 +337,7 @@ void _integration(String description, void body(), [Function testFn]) {
       d.file('version', '0.1.2.3')
     ]).create();
 
-    _sandboxDir = createTempDir();
+    _sandboxDir = createSystemTempDir();
     d.defaultRoot = sandboxDir;
     currentSchedule.onComplete.schedule(() => deleteEntry(_sandboxDir),
         'deleting the sandbox directory');