Add an environment variable toggle to control new service protocol auth token

runtime/observatory/tests/service/auth_token_test.dart

Index: runtime/observatory/tests/service/auth_token_test.dart
diff --git a/runtime/observatory/tests/service/developer_server_control_test.dart b/runtime/observatory/tests/service/auth_token_test.dart
similarity index 73%
copy from runtime/observatory/tests/service/developer_server_control_test.dart
copy to runtime/observatory/tests/service/auth_token_test.dart
index fc1e9405cf4fcd4e0e4cbfa7ff6a0bf5687dbb30..ce75e4f298b595e9a589d3ce7639093771d29205 100644
--- a/runtime/observatory/tests/service/developer_server_control_test.dart
+++ b/runtime/observatory/tests/service/auth_token_test.dart
@@ -14,7 +14,11 @@ Future<Null> testeeBefore() async {
   print(await Service.getInfo());
   // Start the web server.
   ServiceProtocolInfo info = await Service.controlWebServer(enable: true);
-  print(info);
+  expect(info.serverUri, isNotNull);
+  // Ensure that we have the auth token in the path segments.
+  expect(info.serverUri.pathSegments.length, greaterThan(1));
+  // Sanity check the length of the auth token.
+  expect(info.serverUri.pathSegments[0].length, greaterThan(8));
 }
 
 var tests = [
@@ -31,4 +35,5 @@ main(args) => runIsolateTests(args,
                               testeeBefore: testeeBefore,
                               // the testee is responsible for starting the
                               // web server.
-                              testeeControlsServer: true);
+                              testeeControlsServer: true,
+                              useAuthToken: true);