Change confuse() for range_analysis3_test to return non-null int

tests/language/range_analysis3_test.dart

 // Copyright (c) 2014, 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.
 
 import "package:expect/expect.dart";
 
-@NoInline() @AssumeDynamic()
-confuse(x) => x;
+@NoInline()
+@AssumeDynamic()
+confuse(x) => x is int ? x : 0;
 
 test1() {
   int x = 0;
   // Give x a range of -1 to 0.
   if (confuse(0) == 1) x = -1;
 
   int y = 0;
   // Give y a range of 0 to 1.
   if (confuse(0) == 1) y = 1;
 
@@ skipping 176 matching lines @@
 }
 
 main() {
   test1();
   test2();
   test3a();
   test3b();
   test4a();
   test4b();
 }