Fix all strong-mode errors and warnings.

lib/src/backend/live_test.dart

 // 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:async';
 
 import 'group.dart';
 import 'state.dart';
 import 'suite.dart';
 import 'test.dart';
@@ skipping 67 matching lines @@
 
   /// A stream that emits a new [AsyncError] whenever an error is caught.
   ///
   /// This will be emit an event after [errors] is updated. These errors are not
   /// guaranteed to have the same types as when they were thrown; for example,
   /// they may need to be serialized across isolate boundaries. The stack traces
   /// will be [Chain]s.
   Stream<AsyncError> get onError;
 
   /// A stream that emits lines printed by the test.
-  Stream<String> onPrint;
+  Stream<String> get onPrint;
 
   /// A [Future] that completes once the test is complete.
   ///
   /// This will complete after [onStateChange] has fired, and after [onError]
   /// has fired if the test completes because of an error. It's the same as the
   /// [Future] returned by [run].
   ///
   /// Note that even once this completes, the test may still be running code
   /// asynchronously. A test is considered complete either once it hits its
   /// first error or when all [expectAsync] callbacks have been called and any
@@ skipping 39 matching lines @@
   ///
   /// This doesn't automatically happen after the test completes because there
   /// may be more asynchronous work going on in the background that could
   /// produce new errors.
   ///
   /// Returns a [Future] that completes once all resources are released *and*
   /// the test has completed. This allows the caller to wait until the test's
   /// tear-down logic has run.
   Future close();
 }