Remove signature classes from the VM.

runtime/vm/message.cc

 // Copyright (c) 2011, 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/message.h"
 
 #include "vm/dart_entry.h"
 #include "vm/json_stream.h"
 #include "vm/object.h"
 #include "vm/port.h"
@@ skipping 185 matching lines @@
                          current->Id());
     message.AddProperty("size", current->len());
     message.AddProperty("index", depth++);
     message.AddPropertyF("_destinationPort", "%" Pd64 "",
         static_cast<int64_t>(current->dest_port()));
     message.AddProperty("_priority",
         Message::PriorityAsString(current->priority()));
     // TODO(johnmccutchan): Move port -> handler map out of Dart and into the
     // VM, that way we can lookup the handler without invoking Dart code.
     msg_handler = DartLibraryCalls::LookupHandler(current->dest_port());
-    if (msg_handler.IsInstance() && Instance::Cast(msg_handler).IsClosure()) {
+    if (msg_handler.IsClosure()) {
       // Grab function from closure.
-      msg_handler = Closure::function(Instance::Cast(msg_handler));
+      msg_handler = Closure::Cast(msg_handler).function();
     }
     if (msg_handler.IsFunction()) {
       const Function& function = Function::Cast(msg_handler);
       message.AddProperty("handler", function);
 
       const Script& script = Script::Handle(function.script());
       if (!script.IsNull()) {
         message.AddLocation(script, function.token_pos(),
                             function.end_token_pos());
       }
     }
   }
 }
 
 }  // namespace dart