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

tests/language/rewrite_assign_test.dart

Index: tests/language/rewrite_assign_test.dart
diff --git a/tests/compiler/dart2js_extra/16407_test.dart b/tests/language/rewrite_assign_test.dart
similarity index 54%
copy from tests/compiler/dart2js_extra/16407_test.dart
copy to tests/language/rewrite_assign_test.dart
index aff1ba337ddab1eb5d219ac635653b48d4f8d1bc..5379a6ca35bf171a8d2f276529597b1355e26a57 100644
--- a/tests/compiler/dart2js_extra/16407_test.dart
+++ b/tests/language/rewrite_assign_test.dart
@@ -4,13 +4,23 @@
 
 import "package:expect/expect.dart";
 
-// Regression test for Issue 16407.
+bar(x,y) {}
 
-void main() {
-  foo(null, true);
-  foo('x', false);
+foo(b) {
+  var x, y;
+  if (b) {
+    x = 1;
+    y = 2;
+  } else {
+    x = 2;
+    y = 1;
+  }
+  bar(x,y);
+  bar(x,y);
+  return x;
 }
 
-var foo = (x, result) {
-  Expect.equals(result, x is Null, '$x is Null');
-};
+main() {
+    Expect.equals(1, foo(true));
+    Expect.equals(2, foo(false));
+}