dart2dart: Logical operators and related rewrite rules in dart_tree.

tests/language/if_flatten2_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';
+
+check_true_true(x, y) {
+    if (x) {
+        if (y) {
+            return true;
+        }
+    }
+    return false;
+}
+
+check_false_true(x, y) {
+    if (x) {
+
+    } else {
+        if (y) {
+            return true;
+        }
+    }
+    return false;
+}
+
+check_true_false(x, y) {
+    if (x) {
+        if (y) {
+
+        } else {
+            return true;
+        }
+    }
+    return false;
+}
+
+check_false_false(x, y) {
+    if (x) {
+
+    } else {
+        if (y) {
+
+        } else {
+            return true;
+        }
+    }
+    return false;
+}
+
+
+main() {
+    Expect.equals(true, check_true_true(true, true));
+    Expect.equals(false, check_true_true(true, false));
+    Expect.equals(false, check_true_true(false, true));
+    Expect.equals(false, check_true_true(false, false));
+
+    Expect.equals(false, check_true_false(true, true));
+    Expect.equals(true, check_true_false(true, false));
+    Expect.equals(false, check_true_false(false, true));
+    Expect.equals(false, check_true_false(false, false));
+
+    Expect.equals(false, check_false_true(true, true));
+    Expect.equals(false, check_false_true(true, false));
+    Expect.equals(true, check_false_true(false, true));
+    Expect.equals(false, check_false_true(false, false));
+
+    Expect.equals(false, check_false_false(true, true));
+    Expect.equals(false, check_false_false(true, false));
+    Expect.equals(false, check_false_false(false, true));
+    Expect.equals(true, check_false_false(false, false));
+}