Make VM accept function values in assert statements.

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.
 
 import 'dart:_internal' as internal;
 import 'dart:convert' show JSON;
 
 patch class Error {
   /* patch */ static String _objectToString(Object object) {
     return Object._toString(object);
   }
 
   /* patch */ static String _stringToSafeString(String string) {
     return JSON.encode(string);
   }
 
   /* patch */ StackTrace get stackTrace => _stackTrace;
 
   StackTrace _stackTrace;
 }
 
 class _AssertionError extends Error implements AssertionError {
   _AssertionError._create(
       this._failedAssertion, this._url, this._line, this._column);
 
   static _throwNew(int assertionStart, int assertionEnd)
       native "AssertionError_throwNew";
 
+  static _handleCondition(condition) {

[hausner, 2016/06/14 17:51:31]

I'd call this function _evaluateCondition(), or something else appropriate if we
combine evaluation and the throw into one.

+    if (condition is Function) return condition();
+    return condition;
+  }
+
   String toString() {
     if (_url == null) {
       return _failedAssertion;
     }
     var columnInfo = "";
     if (_column > 0) {
       // Only add column information if it is valid.
       columnInfo = " pos $_column";
     }
     return "'$_url': Failed assertion: line $_line$columnInfo: "
@@ skipping 297 matching lines @@
       msg_buf.write(
           "NoSuchMethodError: incorrect number of arguments passed to "
           "method named '$memberName'\n"
           "Receiver: $receiver_str\n"
           "Tried calling: $memberName($actualParameters)\n"
           "Found: $memberName($formalParameters)");
     }
     return msg_buf.toString();
   }
 }