Fix win64 build failure on size truncation

mojo/public/bindings/lib/connector.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/bindings/lib/connector.h"
 
 #include <assert.h>
 #include <stdlib.h>
 
 #include <algorithm>
@@ skipping 100 matching lines @@
 }
 
 void Connector::WriteMore() {
   while (!write_queue_.IsEmpty()) {
     const Message* message = write_queue_.Peek();
 
     MojoResult rv = WriteMessage(message_pipe_,
                                  message->data,
                                  message->data->header.num_bytes,
                                  message->handles.data(),
-                                 message->handles.size(),
+                                 static_cast<uint32_t>(message->handles.size()),
                                  MOJO_WRITE_MESSAGE_FLAG_NONE);
     if (rv == MOJO_RESULT_OK) {
       // TODO(darin): Handles were successfully transferred, and so we need
       // to take care not to Close them here.
       write_queue_.Pop();
       continue;  // Write another message.
     }
 
     error_ = true;
     break;
@@ skipping 21 matching lines @@
 }
 
 void Connector::Callback::OnHandleReady(MojoResult result) {
   assert(owner_);
   Connector* owner = NULL;
   std::swap(owner, owner_);
   owner->OnHandleReady(this, result);
 }
 
 }  // namespace mojo