Revert "Compile-time error if mixin class has a fact

runtime/vm/class_finalizer.cc

 // Copyright (c) 2013, 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/class_finalizer.h"
 
 #include "vm/code_generator.h"
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
@@ skipping 2234 matching lines @@
 
   Array& functions = Array::Handle(zone);
   Function& func = Function::Handle(zone);
   // The parser creates the mixin application class with no functions.
   ASSERT((functions = cls.functions(), functions.Length() == 0));
   // Now clone the functions from the mixin class.
   functions = mixin_cls.functions();
   const intptr_t num_functions = functions.Length();
   for (intptr_t i = 0; i < num_functions; i++) {
     func ^= functions.At(i);
-    if (func.IsFactory() || func.IsGenerativeConstructor()) {
+    if (func.IsGenerativeConstructor()) {
       // A mixin class must not have explicit constructors.
       if (!func.IsImplicitConstructor()) {
-        const char* ctr_kind = func.IsFactory() ? "factory" : "constructor";
         const Script& script = Script::Handle(cls.script());
         const Error& error = Error::Handle(
             LanguageError::NewFormatted(Error::Handle(),
                 script, func.token_pos(), Report::AtLocation,
                 Report::kError, Heap::kNew,
-                "%s '%s' is illegal in mixin class %s",
-                ctr_kind,
+                "constructor '%s' is illegal in mixin class %s",
                 String::Handle(func.PrettyName()).ToCString(),
                 String::Handle(zone, mixin_cls.Name()).ToCString()));
 
         ReportErrors(error, cls, cls.token_pos(),
                      "mixin class '%s' must not have constructors",
                      String::Handle(zone, mixin_cls.Name()).ToCString());
       }
       continue;  // Skip the implicit constructor.
     }
     if (!func.is_static() &&
@@ skipping 1043 matching lines @@
   ASSERT(fields_array.Length() == ByteBuffer::NumberOfFields());
   field ^= fields_array.At(0);
   ASSERT(field.Offset() == ByteBuffer::data_offset());
   name ^= field.name();
   expected_name ^= String::New("_data");
   ASSERT(String::EqualsIgnoringPrivateKey(name, expected_name));
 #endif
 }
 
 }  // namespace dart