initial sync*, part of #221

test/codegen/expect/syncstar_yieldstar_test.txt

Index: test/codegen/expect/syncstar_yieldstar_test.txt
diff --git a/test/codegen/expect/syncstar_yieldstar_test.txt b/test/codegen/expect/syncstar_yieldstar_test.txt
new file mode 100644
index 0000000000000000000000000000000000000000..7e26f80c734f62aa1ccb24abd2016aeb16baa256
--- /dev/null
+++ b/test/codegen/expect/syncstar_yieldstar_test.txt
@@ -0,0 +1,19 @@
+// Messages from compiling syncstar_yieldstar_test.dart
+info: line 97, column 51 of test/codegen/expect.dart: [DynamicCast] expected (dynamic) will need runtime check to cast to type String
+      String stringDifference = _stringDifference(expected, actual);
+                                                  ^^^^^^^^
+info: line 97, column 61 of test/codegen/expect.dart: [DynamicCast] actual (dynamic) will need runtime check to cast to type String
+      String stringDifference = _stringDifference(expected, actual);
+                                                            ^^^^^^
+info: line 372, column 14 of test/codegen/expect.dart: [DynamicInvoke] check(e) requires dynamic invoke
+        if (!check(e)) {
+             ^^^^^^^^
+info: line 28, column 53 of test/codegen/syncstar_yieldstar_test.dart: [DynamicCast] foo().take(9).toList() (dynamic) will need runtime check to cast to type List<dynamic>
+  Expect.listEquals([1, 2, 3, null, 1, 1, 2, 3, 5], foo().take(9).toList());
+                                                    ^^^^^^^^^^^^^^^^^^^^^^
+info: line 28, column 53 of test/codegen/syncstar_yieldstar_test.dart: [DynamicInvoke] foo().take(9).toList() requires dynamic invoke
+  Expect.listEquals([1, 2, 3, null, 1, 1, 2, 3, 5], foo().take(9).toList());
+                                                    ^^^^^^^^^^^^^^^^^^^^^^
+info: line 28, column 53 of test/codegen/syncstar_yieldstar_test.dart: [DynamicInvoke] foo().take(9) requires dynamic invoke
+  Expect.listEquals([1, 2, 3, null, 1, 1, 2, 3, 5], foo().take(9).toList());
+                                                    ^^^^^^^^^^^^^