Fix all strong-mode errors and warnings.

lib/src/runner/load_suite.dart

Index: lib/src/runner/load_suite.dart
diff --git a/lib/src/runner/load_suite.dart b/lib/src/runner/load_suite.dart
index 08cbda308964aeb477ac0eef4f55dcdd84a5fc67..97a2ba40bd45a5c1d89ac00e371399708c835d7d 100644
--- a/lib/src/runner/load_suite.dart
+++ b/lib/src/runner/load_suite.dart
@@ -65,7 +65,7 @@ class LoadSuite extends Suite implements RunnerSuite {
   /// If the the load test is closed before [body] is complete, it will close
   /// the suite returned by [body] once it completes.
   factory LoadSuite(String name, body(), {String path, TestPlatform platform}) {
-    var completer = new Completer.sync();
+    var completer = new Completer<Pair<RunnerSuite, Zone>>.sync();
     return new LoadSuite._(name, () {
       var invoker = Invoker.current;
       invoker.addOutstandingCallback();
@@ -129,6 +129,11 @@ class LoadSuite extends Suite implements RunnerSuite {
   LoadSuite._changeSuite(LoadSuite old, this._suiteAndZone)
       : super(old.group, path: old.path, platform: old.platform);
 
+  /// A constructor used by [filter].
+  LoadSuite._filtered(LoadSuite old, Group filtered)
+      : _suiteAndZone = old._suiteAndZone,
+        super(old.group, path: old.path, platform: old.platform);
+
   /// Creates a new [LoadSuite] that's identical to this one, but that
   /// transforms [suite] once it's loaded.
   ///
@@ -161,5 +166,11 @@ class LoadSuite extends Suite implements RunnerSuite {
     throw 'unreachable';
   }
 
+  LoadSuite filter(bool callback(Test test)) {
+    var filtered = this.group.filter(callback);
+    if (filtered == null) filtered = new Group.root([], metadata: metadata);
+    return new LoadSuite._filtered(this, filtered);
+  }
+
   Future close() async {}
 }