Allow the list of type parameters in the default factory clause to be omitted.

runtime/vm/parser.cc

 // 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.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 2786 matching lines @@
         Array::Handle(factory_class.type_parameters());
     const intptr_t num_type_params = factory_class.NumTypeParameters();
     bool mismatch = interface.NumTypeParameters() != num_type_params;
     for (intptr_t i = 0; !mismatch && (i < num_type_params); i++) {
       interface_type_param_name ^= interface_type_param_names.At(i);
       factory_type_param_name ^= factory_type_param_names.At(i);
       if (!interface_type_param_name.Equals(factory_type_param_name)) {
         mismatch = true;
       }
     }
-    if (mismatch) {
+    // The list of type parameters in the default factory clause can be omitted.
+    if (mismatch && (num_type_params > 0)) {
       const String& interface_name = String::Handle(interface.Name());
       const String& factory_name = String::Handle(factory_class.Name());
       ErrorMsg(factory_pos,
                "mismatch in number or names of type parameters between "
                "interface '%s' and default factory class '%s'.\n",
                interface_name.ToCString(),
                factory_name.ToCString());
     }
   }
 
@@ skipping 4882 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart