Migrate "lib_2/developer" to NNBD.

Close #40140.

Change-Id: I897a486f7b1f421f3691b83b10b9f18837199e82
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/132042
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Leaf Petersen <leafp@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>

tests/lib/developer/inspect_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2015, 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 'dart:developer';
+import 'package:expect/expect.dart';
+
+class Point {
+  int x, y;
+  Point(this.x, this.y);
+}
+
+void main() {
+  var p_in = new Point(3, 4);
+  var p_out = inspect(p_in);
+  Expect.isTrue(identical(p_in, p_out));
+}

tests/lib/developer/timeline_test.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2015, 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 'dart:developer';
+import 'package:expect/expect.dart';
+
+void testUnbalancedStartFinish() {
+  Timeline.startSync('A');
+  Timeline.finishSync();
+
+  bool exceptionCaught = false;
+  try {
+    Timeline.finishSync();
+  } catch (e) {
+    exceptionCaught = true;
+  }
+  Expect.isTrue(exceptionCaught);
+}
+
+void main() {
+  testUnbalancedStartFinish();
+}