dart2dart: Test cases for better code coverage in dart_tree rewritings.

tests/language/rewrite_if_empty_then_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";
+
+var global = 0;
+
+effect() {
+    global = 1;
+}
+baz(b) { return b; }
+
+foo(b) {
+    if (b) {
+        // do nothing
+    } else {
+        effect();
+    }
+    return baz(b);
+}
+
+foo2(b) {
+    if (b) {
+        // do nothing (but implicit return may get inlined up here)
+    } else {
+        effect();
+    }
+}
+
+main() {
+    global = 0;
+    Expect.equals(true, foo(true));
+    Expect.equals(0, global);
+
+    global = 0;
+    Expect.equals(false, foo(false));
+    Expect.equals(1, global);
+
+    global = 0;
+    foo2(true);
+    Expect.equals(0, global);
+
+    global = 0;
+    foo2(false);
+    Expect.equals(1, global);
+}