Allow arity checks on dynamic function types

test/dart_codegen/expect/async/stream_impl.dart

 part of dart.async;
  abstract class _EventSink<T> {void _add(T data);
  void _addError(Object error, StackTrace stackTrace);
  void _close();
 }
  abstract class _EventDispatch<T> {void _sendData(T data);
  void _sendError(Object error, StackTrace stackTrace);
  void _sendDone();
 }
  class _BufferingStreamSubscription<T> implements StreamSubscription<T>, _EventSink<T>, _EventDispatch<T> {static const int _STATE_CANCEL_ON_ERROR = 1;
@@ skipping 167 matching lines @@
  _state |= _STATE_IN_CALLBACK;
  _zone.runUnaryGuarded(_onData, data);
  _state &= ~_STATE_IN_CALLBACK;
  _checkState(wasInputPaused);
 }
  void _sendError(var error, StackTrace stackTrace) {
 assert (!_isCanceled); assert (!_isPaused); assert (!_inCallback); bool wasInputPaused = _isInputPaused;
  void sendError() {
 if (_isCanceled && !_waitsForCancel) return; _state |= _STATE_IN_CALLBACK;
  if (_onError is ZoneBinaryCallback) {
-  _zone.runBinaryGuarded(DEVC$RT.cast(_onError, Function, __t95, "CastGeneral", """line 358, column 32 of dart:async/stream_impl.dart: """, _onError is __t95, false), error, stackTrace);
+  _zone.runBinaryGuarded(DEVC$RT.cast(_onError, Function, __t95, "CastGeneral", """line 358, column 32 of dart:async/stream_impl.dart: """, _onError is __t95, true), error, stackTrace);
   }
  else {
-  _zone.runUnaryGuarded(DEVC$RT.cast(_onError, Function, __t92, "CastGeneral", """line 360, column 31 of dart:async/stream_impl.dart: """, _onError is __t92, false), error);
+  _zone.runUnaryGuarded(DEVC$RT.cast(_onError, Function, __t92, "CastGeneral", """line 360, column 31 of dart:async/stream_impl.dart: """, _onError is __t92, true), error);
   }
  _state &= ~_STATE_IN_CALLBACK;
 }
  if (_cancelOnError) {
 _state |= _STATE_WAIT_FOR_CANCEL;
  _cancel();
  if (_cancelFuture is Future) {
   _cancelFuture.whenComplete(sendError);
   }
  else {
@@ skipping 452 matching lines @@
  _subscription.pause();
  _futureOrPrefetch = null;
  _state = _STATE_EXTRA_DONE;
 }
 }
  typedef void __t87<T>(T __u88);
  typedef void __t89(dynamic __u90);
  typedef dynamic __t92(dynamic __u93);
  typedef dynamic __t95(dynamic __u96, dynamic __u97);
  typedef void __t99(StreamSubscription<dynamic> __u100);