Fix bad type-inferrence for logical expressions.

tests/language/logical_expression5_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';
+
+bool nonInlinedNumTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedNumTypeCheck(object);
+  }
+  return object is num;
+}
+
+bool nonInlinedStringTypeCheck(Object object) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) {
+    return nonInlinedStringTypeCheck(object);
+  }
+  return object is String;
+}
+
+int confuse(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 42) return confuse(x - 1);
+  return x;
+}
+
+main() {
+  var o = [ "foo", 499 ][confuse(0)];
+
+  // The is-checks in the '!' must not be propagated to the if-body, but
+  // the second is-check should.
+  if (!(o is num) && o is String) {
+    Expect.isFalse((nonInlinedNumTypeCheck(o)));
+    Expect.isTrue((nonInlinedStringTypeCheck(o)));
+  }
+}