Typing fixes to eliminate casts/dcalls

test/dart_codegen/expect/async/stream_pipe.dart

 part of dart.async;
  _runUserCode(userCode(), onSuccess(value), onError(error, StackTrace stackTrace)) {
   try {
     onSuccess(userCode());
     }
    catch (e, s) {
     AsyncError replacement = Zone.current.errorCallback(e, s);
      if (replacement == null) {
       onError(e, s);
       }
@@ skipping 112 matching lines @@
 sink._add(inputEvent);
 }
 }
 }
  typedef T _Transformation<S, T>(S value);
  class _MapStream<S, T> extends _ForwardingStream<S, T> {final _Transformation _transform;
  _MapStream(Stream<S> source, T transform(S event)) : this._transform = transform, super(source);
  void _handleData(S inputEvent, _EventSink<T> sink) {
 T outputEvent;
  try {
-outputEvent = ((__x63) => DEVC$RT.cast(__x63, dynamic, T, "CompositeCast", """line 235, column 21 of dart:async/stream_pipe.dart: """, __x63 is T, false))(_transform(inputEvent));
+outputEvent = ((__x58) => DEVC$RT.cast(__x58, dynamic, T, "CompositeCast", """line 235, column 21 of dart:async/stream_pipe.dart: """, __x58 is T, false))(_transform(inputEvent));
 }
  catch (e, s) {
 _addErrorWithReplacement(sink, e, s);
  return;}
  sink._add(outputEvent);
 }
 }
  class _ExpandStream<S, T> extends _ForwardingStream<S, T> {final _Transformation<S, Iterable<T>> _expand;
  _ExpandStream(Stream<S> source, Iterable<T> expand(S event)) : this._expand = expand, super(source);
  void _handleData(S inputEvent, _EventSink<T> sink) {
@@ skipping 128 matching lines @@
 _addErrorWithReplacement(sink, e, s);
  return null;
 }
  if (!isEqual) {
 sink._add(inputEvent);
  _previous = inputEvent;
 }
 }
 }
 }