Reapply "Refactor type propagation."

frog/tests/leg/src/TypeInference3Test.dart

Index: frog/tests/leg/src/TypeInference3Test.dart
diff --git a/frog/tests/leg/src/TypeInference3Test.dart b/frog/tests/leg/src/TypeInference3Test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6f025185af9a19ef03432436346390f11c127025
--- /dev/null
+++ b/frog/tests/leg/src/TypeInference3Test.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2011, 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("compiler_helper.dart");
+
+final String TEST_ONE = @"""
+sum(param0, param1) {
+  var sum = 0;
+  for (var i = param0; i < param1; i += 1) sum = sum + i;
+  return sum;
+}
+""";
+
+main() {
+  String generated = compile(TEST_ONE, 'sum');
+  regexp = const RegExp("typeof param0 !== 'number'");
+  Expect.isTrue(regexp.hasMatch(generated));
+}