Fix Dart 1.17 strong-mode warnings.

test/stream_completer_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 "package:async/async.dart" show StreamCompleter;
 import "package:test/test.dart";
 
 import "utils.dart";
@@ skipping 112 matching lines @@
     completer.stream.listen(
         unreachable("data"),
         onError: unreachable("error"),
         onDone: done.complete);
     completer.setEmpty();
     await done.future;
   });
 
   test("source stream isn't listened to until completer stream is", () async {
     var completer = new StreamCompleter();
-    var controller;
+    StreamController controller;
     controller = new StreamController(onListen: () {
       scheduleMicrotask(controller.close);
     });
 
     completer.setSourceStream(controller.stream);
     await flushMicrotasks();
     expect(controller.hasListener, isFalse);
     var subscription = completer.stream.listen(null);
     expect(controller.hasListener, isTrue);
     await subscription.asFuture();
@@ skipping 130 matching lines @@
   test("listening more than once before setting stream", () async {
     var completer = new StreamCompleter();
     completer.stream.toList();
     expect(() => completer.stream.toList(), throwsStateError);
   });
 
   test("setting onData etc. before and after setting stream", () async {
     var completer = new StreamCompleter();
     var controller = new StreamController();
     var subscription = completer.stream.listen(null);
-    var lastEvent = 0;
+    Object lastEvent = 0;
     subscription.onData((value) => lastEvent = value);
     subscription.onError((value) => lastEvent = "$value");
     subscription.onDone(() => lastEvent = -1);
     completer.setSourceStream(controller.stream);
     await flushMicrotasks();
     controller.add(1);
     await flushMicrotasks();
     expect(lastEvent, 1);
     controller.addError(2);
     await flushMicrotasks();
@@ skipping 74 matching lines @@
 
 Stream<int> createStream() async* {
   yield 1;
   await flushMicrotasks();
   yield 2;
   await flushMicrotasks();
   yield 3;
   await flushMicrotasks();
   yield 4;
 }