Fix most strong mode warnings.

lib/src/stream_group.dart

Index: lib/src/stream_group.dart
diff --git a/lib/src/stream_group.dart b/lib/src/stream_group.dart
index 6239fc232fe2a8abf0f29009b821ec063278a7a3..0d73f8177aad1835d351ac021508cf00f6e0031d 100644
--- a/lib/src/stream_group.dart
+++ b/lib/src/stream_group.dart
@@ -53,8 +53,8 @@ class StreamGroup<T> implements Sink<Stream<T>> {
   ///
   /// This is equivalent to adding [streams] to a group, closing that group, and
   /// returning its stream.
-  static Stream merge(Iterable<Stream> streams) {
-    var group = new StreamGroup();
+  static Stream/*<T>*/ merge/*<T>*/(Iterable<Stream/*<T>*/> streams) {
+    var group = new StreamGroup/*<T>*/();
     streams.forEach(group.add);
     group.close();
     return group.stream;
@@ -192,7 +192,7 @@ class StreamGroup<T> implements Sink<Stream<T>> {
   /// Starts actively forwarding events from [stream] to [_controller].
   ///
   /// This will pause the resulting subscription if [this] is paused.
-  StreamSubscription _listenToStream(Stream stream) {
+  StreamSubscription<T> _listenToStream(Stream<T> stream) {
     var subscription = stream.listen(
         _controller.add,
         onError: _controller.addError,