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

device/serial/test_serial_io_handler.cc

Index: device/serial/test_serial_io_handler.cc
diff --git a/device/serial/test_serial_io_handler.cc b/device/serial/test_serial_io_handler.cc
index bf8fbb1334ac6840795a31bad358df60917b8a1f..f73197f8582caf3e6ee5fdc56502c7eb3cea827c 100644
--- a/device/serial/test_serial_io_handler.cc
+++ b/device/serial/test_serial_io_handler.cc
@@ -53,8 +53,8 @@ void TestSerialIoHandler::CancelReadImpl() {
 void TestSerialIoHandler::WriteImpl() {
   DCHECK(pending_read_buffer());
   DCHECK_LE(pending_write_buffer_len(), pending_read_buffer_len());
-  memcpy(pending_read_buffer()->data(),
-         pending_write_buffer()->data(),
+  memcpy(pending_read_buffer(),
+         pending_write_buffer(),
          pending_write_buffer_len());
   QueueReadCompleted(pending_write_buffer_len(), serial::RECEIVE_ERROR_NONE);
   QueueWriteCompleted(pending_write_buffer_len(), serial::SEND_ERROR_NONE);