Fix bad type-inferrence for logical expressions.

tests/language/logical_expression2_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";
+
+// Regression test for issue 17149.
+
+int globalCounter = 0;
+
+void nonInlinedUse(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) nonInlinedUse(object);
+  if (object is! String) globalCounter++;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(1)];
+
+  // The `o is String` check in the rhs of the logical or must not be
+  // propagated to the `if` body.
+  if ((o is num) ||
+      (o is String && true)) {
+    nonInlinedUse(o);
+  }
+  Expect.equals(1, globalCounter);
+}