Implement type inference for conventional for-loops.

pkg/front_end/testcases/implicit_scope_test.dart.strong.expect

Index: pkg/front_end/testcases/implicit_scope_test.dart.strong.expect
diff --git a/pkg/front_end/testcases/implicit_scope_test.dart.strong.expect b/pkg/front_end/testcases/implicit_scope_test.dart.strong.expect
index 3b8a5c77f7ca10529a0d4c967103a382b29b9d85..3af9646aa57860e9b6812e8b3b20526090e5116c 100644
--- a/pkg/front_end/testcases/implicit_scope_test.dart.strong.expect
+++ b/pkg/front_end/testcases/implicit_scope_test.dart.strong.expect
@@ -27,7 +27,7 @@ class ImplicitScopeTest extends core::Object {
     }
     exp::Expect::equals("foo", a);
     exp::Expect::equals(null, b);
-    for (core::int i = 0; i.<(10); i = i.+(1)) {
+    for (core::int i = 0; i.{core::num::<}(10); i = i.{core::num::+}(1)) {
       dynamic a = "bar";
       dynamic b = "baz";
     }