Convert SerialIoHandler to use buffer interfaces for I/O API methods.

device/serial/serial_io_handler_win.cc

Index: device/serial/serial_io_handler_win.cc
diff --git a/device/serial/serial_io_handler_win.cc b/device/serial/serial_io_handler_win.cc
index 1ab4f88aa81fb1501d1f719d167448b23d920ded..ac669ad31917bfc990223bb93c087963430fa7ea 100644
--- a/device/serial/serial_io_handler_win.cc
+++ b/device/serial/serial_io_handler_win.cc
@@ -217,7 +217,7 @@ void SerialIoHandlerWin::WriteImpl() {
   DCHECK(file().IsValid());
 
   BOOL ok = ::WriteFile(file().GetPlatformFile(),
-                        pending_write_buffer()->data(),
+                        pending_write_buffer(),
                         pending_write_buffer_len(),
                         NULL,
                         &write_context_->overlapped);
@@ -260,7 +260,7 @@ void SerialIoHandlerWin::OnIOCompleted(
       ReadCompleted(0, serial::RECEIVE_ERROR_SYSTEM_ERROR);
     } else if (pending_read_buffer()) {
       BOOL ok = ::ReadFile(file().GetPlatformFile(),
-                           pending_read_buffer()->data(),
+                           pending_read_buffer(),
                            pending_read_buffer_len(),
                            NULL,
                            &read_context_->overlapped);