Fix tests to avoid analyzer warnings.

tests/html/js_typed_interop_type3_test.dart

Index: tests/html/js_typed_interop_type3_test.dart
diff --git a/tests/html/js_typed_interop_type3_test.dart b/tests/html/js_typed_interop_type3_test.dart
index f20bc2077695787b79d12b5ee25fd0457d66b627..f32d9f3e60349ca781d5fbf80243d7732dbb0990 100644
--- a/tests/html/js_typed_interop_type3_test.dart
+++ b/tests/html/js_typed_interop_type3_test.dart
@@ -65,7 +65,8 @@ function A(foo) {
 
 void expectValueOrTypeError(f(), value) {
   try {
-    String i = 0; // Test for checked mode.
+    var i = 0;
+    String s = i; // Test for checked mode.
     Expect.equals(f(), value);
   } on TypeError catch (error) {
     Expect.throws(f, (ex) => ex is TypeError);