Fix #14144 confusing error message misusing a callable object

runtime/lib/errors_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 @patch
 class Error {
   @patch
   static String _objectToString(Object object) {
     return Object._toString(object);
   }
@@ skipping 294 matching lines @@
         {
           if (_receiver == null) {
             if (args_mismatch) {
               msg_buf.writeln("The null object does not have a $type_str "
                   "'$memberName'$args_message.");
             } else {
               msg_buf
                   .writeln("The $type_str '$memberName' was called on null.");
             }
           } else {
-            if (_receiver is Function) {
+            if (_receiver.runtimeType == Function ||

[rmacnak, 2017/03/31 16:36:39]

`_receiver.runtimeType == Function` doesn't match anything because Function is
abstract.


class C {
  call() => 42;
}

main() {
  var c = new C();
  print(c.runtimeType == Function);  // false
  print(c is Function);  // true
}

+                _receiver.runtimeType == _Closure) {
               msg_buf.writeln("Closure call with mismatched arguments: "
                   "function '$memberName'");
             } else if (_receiver is _Type && memberName == "call") {
               is_type_call = true;
               String name = _receiver.toString();
               msg_buf.writeln("Attempted to use type '$name' as a function. "
                   "Since types do not define a method 'call', this is not "
                   "possible. Did you intend to call the $name constructor and "
                   "forget the 'new' operator?");
             } else {
@@ skipping 62 matching lines @@
 
     return msg_buf.toString();
   }
 }
 
 class _CompileTimeError extends Error {
   final String _errorMsg;
   _CompileTimeError(this._errorMsg);
   String toString() => _errorMsg;
 }