tools/battor_agent: Fixes a VS warning in battor_connection_impl.cc

tools/battor_agent/battor_connection_impl.cc

 // Copyright 2015 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 "tools/battor_agent/battor_connection_impl.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "device/serial/buffer.h"
 #include "device/serial/serial_io_handler.h"
@@ skipping 138 matching lines @@
 }
 
 void BattOrConnectionImpl::BeginReadBytes(size_t max_bytes_to_read) {
   pending_read_buffer_ =
       make_scoped_refptr(new net::IOBuffer(max_bytes_to_read));
 
   auto on_receive_buffer_filled =
       base::Bind(&BattOrConnectionImpl::OnBytesRead, AsWeakPtr());
 
   io_handler_->Read(make_scoped_ptr(new device::ReceiveBuffer(
-      pending_read_buffer_, max_bytes_to_read, on_receive_buffer_filled)));
+      pending_read_buffer_, static_cast<uint32_t>(max_bytes_to_read),
+      on_receive_buffer_filled)));
 }
 
 void BattOrConnectionImpl::OnBytesRead(int bytes_read,
                                        device::serial::ReceiveError error) {
   if (bytes_read == 0 || error != device::serial::ReceiveError::NONE) {
     // If we didn't have a message before, and we weren't able to read any
     // additional bytes, then there's no valid message available.
     EndReadBytes(false, BATTOR_MESSAGE_TYPE_CONTROL, nullptr);
     return;
   }
@@ skipping 84 matching lines @@
 }
 
 void BattOrConnectionImpl::OnBytesSent(int bytes_sent,
                                        device::serial::SendError error) {
   bool success = (error == device::serial::SendError::NONE) &&
                  (pending_write_length_ == static_cast<size_t>(bytes_sent));
   listener_->OnBytesSent(success);
 }
 
 }  // namespace battor