kernel -> ssa: add tests for other simple operators

tests/compiler/dart2js/kernel/binary_operators_test.dart

Index: tests/compiler/dart2js/kernel/binary_operators_test.dart
diff --git a/tests/compiler/dart2js/kernel/binary_operators_test.dart b/tests/compiler/dart2js/kernel/binary_operators_test.dart
index 1afaeb8a4b1c38f441e2c3aebd5b1b0d2680d85e..96f3fdb0621c196c159577b6fe9e4f6d915bc9cc 100644
--- a/tests/compiler/dart2js/kernel/binary_operators_test.dart
+++ b/tests/compiler/dart2js/kernel/binary_operators_test.dart
@@ -11,5 +11,17 @@ main() {
     test('plus on ints', () {
       return check('main() { return 1 + 2; }');
     });
+    test('plus on strings', () {
+      return check('main() { return "a" + "b"; }');
+    });
+    test('plus on non-constants', () {
+      String code = '''
+        foo() => 1;
+        main() => foo() + foo();''';
+      return check(code);
+    });
+    test('other arithmetic operators', () {
+      return check('main() { return 1 + 2 * 3 - 4 / 5 % 6; }');
+    });
   });
 }