Add APIs for asserting the types of transformers.

CHANGELOG.md

+## 1.11.0
+
+* Add a `typedStreamTransformer()` function. This wraps an untyped
+  `StreamTransformer` with the correct type parameters, and asserts the types of
+  events as they're emitted from the transformed stream.
+
+* Add a `StreamSinkTransformer.typed()` static method. This wraps an untyped
+  `StreamSinkTransformer` with the correct type parameters, and asserts the
+  types of arguments passed in to the resulting sink.
+
 ## 1.10.0
 
 * Add `DelegatingFuture.typed()`, `DelegatingStreamSubscription.typed()`,
   `DelegatingStreamConsumer.typed()`, `DelegatingSink.typed()`,
   `DelegatingEventSink.typed()`, and `DelegatingStreamSink.typed()` static
   methods. These wrap untyped instances of these classes with the correct type
   parameter, and assert the types of values as they're accessed.
 
 * Add a `DelegatingStream` class. This is behaviorally identical to `StreamView`
   from `dart:async`, but it follows this package's naming conventions and
@@ skipping 107 matching lines @@
 - Added a `StreamSplitter` class for splitting a stream into multiple new
   streams.
 
 ## 1.1.1
 
 - Updated SDK version constraint to at least 1.9.0.
 
 ## 1.1.0
 
 - ChangeLog starts here.