Address Ivan's review comments.

runtime/lib/isolate.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 "platform/assert.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 240 matching lines @@
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len));
   OS::SNPrint(chars, len, kFormat, script_name, class_name, func_name);
   return chars;
 }
 
 
 DEFINE_NATIVE_ENTRY(IsolateNatives_start, 2) {
   Isolate* preserved_isolate = Isolate::Current();
   GET_NATIVE_ARGUMENT(Instance, runnable, arguments->At(0));
+  // arguments->At(1) unused.
   const Class& runnable_class = Class::Handle(runnable.clazz());
   const char* class_name = String::Handle(runnable_class.Name()).ToCString();
   const Library& library = Library::Handle(runnable_class.library());
   ASSERT(!library.IsNull());
   const char* library_url = String::Handle(library.url()).ToCString();
   intptr_t port_id = 0;
   LongJump jump;
   bool init_successful = true;
   Isolate* spawned_isolate = NULL;
   void* callback_data = preserved_isolate->init_callback_data();
@@ skipping 81 matching lines @@
   // TODO(iposva): Allow for arbitrary messages to be sent.
   GET_NATIVE_ARGUMENT(Instance, obj, arguments->At(2));
   uint8_t* data = SerializeObject(obj);
 
   // TODO(turnidge): Throw an exception when the return value is false?
   PortMap::PostMessage(new Message(
       send_id.Value(), reply_id.Value(), data, Message::kNormalPriority));
 }
 
 }  // namespace dart