Rationalize coercions

test/dart_codegen/expect/async/stream_transformers.dart

 part of dart.async;
  class _EventSinkWrapper<T> implements EventSink<T> {_EventSink _sink;
  _EventSinkWrapper(this._sink);
  void add(T data) {
   _sink._add(data);
   }
  void addError(error, [StackTrace stackTrace]) {
   _sink._addError(error, stackTrace);
   }
  void close() {
@@ skipping 43 matching lines @@
  void _handleData(S data) {
 try {
   _transformerSink.add(data);
   }
  catch (e, s) {
   _addError(e, s);
   }
 }
  void _handleError(error, [stackTrace]) {
 try {
-  _transformerSink.addError(error, DEVC$RT.cast(stackTrace, dynamic, StackTrace, "CastGeneral", """line 127, column 40 of dart:async/stream_transformers.dart: """, stackTrace is StackTrace, true));
+  _transformerSink.addError(error, DEVC$RT.cast(stackTrace, dynamic, StackTrace, "DynamicCast", """line 127, column 40 of dart:async/stream_transformers.dart: """, stackTrace is StackTrace, true));
   }
  catch (e, s) {
   if (identical(e, error)) {
-    _addError(error, DEVC$RT.cast(stackTrace, dynamic, StackTrace, "CastGeneral", """line 130, column 26 of dart:async/stream_transformers.dart: """, stackTrace is StackTrace, true));
+    _addError(error, DEVC$RT.cast(stackTrace, dynamic, StackTrace, "DynamicCast", """line 130, column 26 of dart:async/stream_transformers.dart: """, stackTrace is StackTrace, true));
     }
    else {
     _addError(e, s);
     }
   }
 }
  void _handleDone() {
 try {
   _subscription = null;
    _transformerSink.close();
@@ skipping 13 matching lines @@
  bool get isBroadcast => _stream.isBroadcast;
  _BoundSinkStream(this._stream, this._sinkMapper);
  StreamSubscription<T> listen(void onData(T event), {
 Function onError, void onDone(), bool cancelOnError}
 ) {
 cancelOnError = identical(true, cancelOnError);
  StreamSubscription<T> subscription = ((__x105) => DEVC$RT.cast(__x105, DEVC$RT.type((_SinkTransformerStreamSubscription<dynamic, dynamic> _) {
 }
 ), DEVC$RT.type((StreamSubscription<T> _) {
 }
-), "CastExact", """line 186, column 42 of dart:async/stream_transformers.dart: """, __x105 is StreamSubscription<T>, false))(new _SinkTransformerStreamSubscription(_stream, DEVC$RT.wrap((EventSink<S> f(EventSink<T> __u106)) {
+), "InferableAllocation", """line 186, column 42 of dart:async/stream_transformers.dart: """, __x105 is StreamSubscription<T>, false))(new _SinkTransformerStreamSubscription(_stream, DEVC$RT.wrap((EventSink<S> f(EventSink<T> __u106)) {
 EventSink<S> c(EventSink<T> x0) => f(DEVC$RT.cast(x0, DEVC$RT.type((EventSink<dynamic> _) {
 }
 ), DEVC$RT.type((EventSink<T> _) {
 }
 ), "CastParam", """line 187, column 18 of dart:async/stream_transformers.dart: """, x0 is EventSink<T>, false));
  return f == null ? null : c;
 }
 , _sinkMapper, DEVC$RT.type((__t109<T, S> _) {
 }
 ), __t107, "Wrap", """line 187, column 18 of dart:async/stream_transformers.dart: """, _sinkMapper is __t107), onData, onError, onDone, cancelOnError));
@@ skipping 76 matching lines @@
 }
 }
  typedef EventSink<dynamic> __t107(EventSink<dynamic> __u108);
  typedef EventSink<S> __t109<T, S>(EventSink<T> __u110);
  typedef EventSink<S> __t113<T, S>(EventSink<T> __u114);
  typedef dynamic __t115<T>(EventSink<T> __u116);
  typedef void __t120<S, T>(S __u121, EventSink<T> __u122);
  typedef void __t123(dynamic __u124, EventSink<dynamic> __u125);
  typedef void __t129<T>(Object __u130, StackTrace __u131, EventSink<T> __u132);
  typedef void __t133(dynamic __u134, StackTrace __u135, EventSink<dynamic> __u136);