Fix most strong mode warnings.

lib/src/subscription_stream.dart

Index: lib/src/subscription_stream.dart
diff --git a/lib/src/subscription_stream.dart b/lib/src/subscription_stream.dart
index 4f58c76f8af7dc012c953e6e3e25c89f9147ab42..c448620c5edc6a256aa5e72f50ffc7ad0c555555 100644
--- a/lib/src/subscription_stream.dart
+++ b/lib/src/subscription_stream.dart
@@ -18,7 +18,7 @@ import "delegate/stream_subscription.dart";
 /// If other code is accessing the subscription, results may be unpredictable.
 class SubscriptionStream<T> extends Stream<T> {
   /// The subscription providing the events for this stream.
-  StreamSubscription _source;
+  StreamSubscription<T> _source;
 
   /// Create a single-subscription `Stream` from [subscription].
   ///
@@ -29,7 +29,7 @@ class SubscriptionStream<T> extends Stream<T> {
   /// If the `subscription` doesn't send any `done` events, neither will this
   /// stream. That may be an issue if `subscription` was made to cancel on
   /// an error.
-  SubscriptionStream(StreamSubscription subscription)
+  SubscriptionStream(StreamSubscription<T> subscription)
        : _source = subscription {
     _source.pause();
     // Clear callbacks to avoid keeping them alive unnecessarily.
@@ -48,13 +48,10 @@ class SubscriptionStream<T> extends Stream<T> {
     cancelOnError = (true == cancelOnError);
     var subscription = _source;
     _source = null;
-    var result;
-    if (cancelOnError) {
-      result = new _CancelOnErrorSubscriptionWrapper<T>(subscription);
-    } else {
-      // Wrap the subscription to ensure correct type parameter.
-      result = new DelegatingStreamSubscription<T>(subscription);
-    }
+
+    var result = cancelOnError
+        ? new _CancelOnErrorSubscriptionWrapper<T>(subscription)
+        : subscription;
     result.onData(onData);
     result.onError(onError);
     result.onDone(onDone);